captioning sponsored by newshour productions, llc >> woodruff: good evening, i'm judy woodruff. on the newshour tonight... >> never again! >> woodruff: ...survivorscof the florol shooting and thousands of others demand change to the nation's gun laws as president trump holds a meeting on school safety. then, a city in scotland reflects on the school shooting orthat shook its community than 20 years ago and what it could teach the u.s. about stopping >> you can never say never but i think we've done an awful lot to make our schls safer places and i don't go out the dr with some of the worries american parents undoubtedly have tdray. >> wf: plus, what freely available open-source data and satellite images can tell us about the true power of north korea's nuclear arsenal.

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station from viewers like you. ank you. >> woodruff: calls for action after the school shooting in haorida. in talee and around the dcountry today, students supporters appealed for an end to the bloodshed. william brangham begins our coverage. >> what do we want? >> change! >> when do we wantt? >> now! >> brangham: the chants began as soon as abou100 of the school shooting survivors arrivedstt the floride capital in tallahassee. >> never again! never again! >> brangham: from there, they moved inside to lobby the republican-run legislature for some stronger gun cont >> please, i beg and i demand that every single person in power who hathe ability to change the fear that kids feel going back to scho, that they do something.

>> no longer can you take money from the n.r.a. no longer can you fly under the radar doing whatever it is tha. you want to because we are coming after you. we are coming after every single one of you and demanding that you take action and demanding that you maka change. >> brangham: the crowds outside the capitol grew to thousands for a midday rally. there they heard an outpouringer of and grief, over the killing of 17 at marjory stoneman douglas high school, one week ago today. how many more innocent people have to die before we make a change? a change is overdue. and we are the change. when children act like leaders and leaders act like children you know something is about to change! >> brangham: these snt activists had traveled more than 400 miles, from parkland, in south florida, to press for a range of solutions. one student called for a ban on semi-automatic weapons like the a-r-15 rifle used in the massacre. >> the only purpose of an assault weapon like this is to kill and to kill as many people

as possible. the a-r-15 is not a self-defense weapon. it is rightly so-called an assaults weapon. >> brangham: a day earlier, the florida state house voted against taking up a bill to ban assault weapons. today, the democrawho called for that bill to be debated made an impassionedlea for the students to keep up their fight. >> you are the cavalry we've been waiting for! so to you, let's do it! >> brangham: across e country, thousands of students heeded that call, walking out of classes and chanting slogans demandg tougher gun control. in washington, d., hundreds massed outside the u.s. capitol and the white house. inside the executive mansion, ent trump held a listeni session with high school students and teachers. among them: some who survivedrk the nd attack, as well as others from school shootings at, newtonnecticut, in 2012 and at columbine high in colorado in 1999.

>> we're going to be very strong on background checks. we'll be doiry strong background checks. very strong emphasis on the sntal health ofomebody. >> how is it that easy to buy this type of weapon? how do we not stop in after columbine,fter sandy hook? >> it should have been one school shooting and we should have fixed it! and i'm pisseca e my daughter i'm not going to see again! >> until now the president has been a staunch supporter of gun rights. last year, he signed a law that eliminated an obama-era regulation which made it harder for some mentally-ill people to get guns. the receiving social security benefits for mental illness and who had also been ruled incapable of handling their own finances would be blocked from purchasing weapons. the president signed the law reversing that rule last february.

mr. trump has also repeatedly maintained his aegiance to the national rifle association. last april, he addressed the n.r.a.'s leadership forum in atlanta. >> you came through for me, and i am going to come through for you. >> brangham: the center for responsive politics estimates that during the 2016 election, the n.r.a. spent $30 million to support mr. trump and oppose hillary clinton. during one of the presidential debates, candidate trump argued that strict gun laws duc't htually rgun violence. >> in chicago, whi the toughest gun laws in the united states, prably you could say by far, they have more gun violce than any other city. >> brangham: but yesterday, amid the outcry over parkland, the president appeared to soften his stance. >> just a few moments ago i signed aemorandum directing the attorney general to propose regulations to ban all dices at turn legal weapons into machine guns.

>> brangham: democrats likean senator difeinstein of california urged the president to support her legislation banning bump stocks and to encourage his fellow republikins to stop bl it. white house spokeswoman sah sanders also said the president is open to improving federal background checks, and possibly setting a minimum age for buying a-r-15-type rifles. for the pbs newshour, i'm william brangham. >> woodruff: the president rlso said today letting trained school workers cry weapons might make attackers think twice and, in his words, solve the problem. we'll return to all of this after the news summary. in the day's other news, president trump charged again that president obama should havo more about russian meddling in the 2016 election. he also questioned why hisen attorneyal, jeff sessions, is not investigating democrats. meanwhile, house and senatede democratic l, nancy pelosi 00d chuck schumer, called for giving the f.b.i. illion

to fight any meddling in the mid-term elections. onties and towns across the nation's mid-secaced severe flooding today, from heavy rain and melting snow. rivers overflowed in michigan, indiana and parts of illinois, submerging rds and neighborhoods. in,oshen, indiana overnightcr ews used boats to rescue people from their homes. and in arkansas, a school bus had to be abandoned today, and a dozen students rescued. in syria, the carnage raged on, in a major assault on rebel-held suburbs east of damascus. human rights monitors now say more than 300 people have been killed, just since sunday, andsa doctorthey are overwhelmed. government air strikes and artillery are blasting t area, and humanitarian groups warned today it's a catastrophe in the making. >> people are terrified. we know that many are seeking shelter in basements and in dugt makeshift shelters.

we know that children are facing the brunt of this crisis and we are very, very worried for the safety of everyone.>> oodruff: meanwhile, in the north of syria, turkey vowedto agaiontinue its offensive against syrian kurdish fighters around afrin. also repeated a warning that nm will attack fighters allied with syria's govt, if they try to aid the kurds. new details today on the deadly wreck of an amtrak train that carried dozens of republican congressmen. the train slammed into a garbage truck on tracks in rural virginia last month. now, theational transportation safety board says the truck had tried to cross after the safety gates came down. one of the workers on the truckd was kin the crash. the president's eldest son is rejecting criticism that he's profiting from his father being in office.un donald trumpr is on a week-long business trip to india

that's raised conflict of interest questions. but he told india's cnbcaf liate that his family is actually missing out on opportunities. >> when people talk about it these days it's profiteering from the presidency and all this nonsense. it's like wait a minute-- i can't do deals? i've spent over a decade creating relationships. and we could do so many more and we are not doing those. 'but no one wants to talk about those kind of deals. it's sort of a shame. because we put on all these impositions on ourselves and essentially got no credit for actually doing that and for doing the right thing. >> woodruff: the president's son is marketing trump brand lury homes in india. as president-etrct, the elder p had pledged his real estate business would conduct nh new deale in office. questions today about whetheria first lady melrump sponsored her parents for legaln resident statuhe united states. t's a process that presid trump has condemned as "chain migration." "the washington post" reportsia

the slovnationals have their green cards, and will soon become u.s. citizens. the report quotes immigration experts as saying mrs. trump's sponsorship appears be the "only reasonable way" that could happen. on wall street today, stocks swooned late, after minutes from the federal reserve's latest meeting signaled more interest rate hikes. the dow jones industrial average lost nearly 167 points to close at 24,797. the nasd the s&p 500 slipped almost 15. and,t the winter olympics in south korea, an important day for american skiers. jessica diggins won the first u.s. gold medal, ever, in cross- country skiing. and lindsey vonn took bronze in the women's downhill. at 33, she's the oldest woman ever to medal in alpine skiing. still to come on the newshour:th e backlash parkland, florida,

students are facing for speaking out about gun laws.ot how nd tackled gun violence after a school shooting in the 1990s.th rememberinlife and legacy of billy graham, plus, much more. >> woodruff: as we said at the beginning of the program, student-led rallies have picked up a momentu florida and around the country what should be dt-e about assayle weapons and other kinds of guns. there were rallies here in washington as well today, inhe front ofhite house and near the capitol. two students who participated after a school walkout join me now. camille richter is a senior at mclean high school in mclean, virginia.

and jake bennett is a senior at h.b. woodlawn in arlington, virginia. and thank you to both of you for coming out here to the studio to talk to us. jake, i'm going to sta you.ith youralked five miles fr school to the white house. why did you want to be a part of this today? >> because we live so close to d.c., we felt it wouldn't be the same if we just waked outside, if we just walked to a courthouse, which is where our public school headquarters are. we felt driven to march to the white house and to really show we would go this far to voice our discontent and our anger with congress. >> woodruff: and and, camile, wy is this so important to you? >> i am sick of going to school every day and being scared for my life and my friends' lives.

we live in a relatively safe part of virginia in mclean and it's silly we live in a first-world country and, still, first graders, second graders, young kids all through high schoolers are afraid of going to school, and they're afraid of what's going to happen to them. it's not right and it really needs to stop. >> woodruff: you were sying you feel strongly that something has to be done. do you have an idea right now o what you think it should be? >> i think that univerl background checks need to be implemented to buy a gun, and i think that we shod ban assault rifles again. arey were banned for ten and that really did work. there's no need for american civilians to have chine of war. they're not used for hunting or protection, they're used for murder, and i think those are two steps in the right direction. you know, background checks are very fast, they take two minutes, and they would really .ave a lot of lives, my opini

>> woodruff: yet, a lot ofle peay since we haven't had that legislation since it expired argue people should beto allowe buy any kind of gun they have to. >> it was ridiculou in virginia we can only buy one gun a month which some complained is tooic resve. i have a lot of family from wisconsin, hunters.ha been around guns for a long time. i know what it's like. you shoot a gun, you live in virginia, it's a pretty regular ing. but there's a difference between a hunting riflele and an assault rifle. there's a different between military grade. it's blatantly understand necessary. >> woodruff: jake, you mentioned the assault weapons and one of theh ideasat's being discussed today is putting an age limit on who can buy an ar-15 or another asslt weapon.

would something like that, you think, be acceptable? >> i think part of that would bt acle. i think that an age limit should be implemented but oher restrictions should be added on to it. i really don't believe that anyone needs an air 15 or other assault wea they don't serve any purpose except massacre. it's what the shooters in sandy hook and newtown used and orlando and nowt soneman douglas. it's unnecessary. >> woodruff: camile, there haveeen proposals there b more guns in schools to protect sudents, that teachers or others be trained and armed to protect students. >> i think it'xpensive and u unnecessary. ow, how much money does it cost to give every teacher and potentially the students the training and weaponry they need in order to protect themselves?

it feels like there is an easier solution to the problem that people anlawmakers are kind of avoiding. >> woodruff: jake, i know you j were ast watching some of the discussion inside the white house, president trump ivited students and some parents who have been through tese tragedies, and educators, do you feel like the message is getting throh to the people who can make a difference? the message is the flrida students are sending, you know, that we were sending, what students all across america are sending, parents, teachers, everyday people are trying to send to congress and to the president are that, you know,ng ss needs to stop saying yes to the n.r.a. and start saying yes to the american children and safety and schools. i think that's the message we were trying to send. i think what we did tod was set forward a motion that will keep, you kno it will kep building momentum until it does make a change.

>> woodruff: wt about that, camile? because there have been school shootings and protests before, t it hasn't lasted or there have been a little bit of change but not a change, these things keep hap. >> we elected congress to be the representatives of the people, not to be the representatives of big lobby firms and of the n.r.a. it feels like when your legislature andpresentatives ignore the epidemic of shootings going on across the u.s it makes you wonder who they are working for. you know, you want to be represented. you want your voice to be heard. so... >> woodruff: and, you know, some say, well, these young pele feel strongly butey're just high school students. >> right. >> woodruff: how much difference can they really make? >> i think we can make aug difference. there has been some talk from some representatives that, yough know, the chool students who are making a stand in florida are plants by the f.b.i. or paid to do this, and it'sly absoluidiculous. again, like we were saying earlier, if you're 18, men are

old enough to b drafted. at 16, at least in virginia, you can buy a cars, which is dangerous within its why can you buy a gun? you can do these things -- it's just -- it doesn't make sense. we have a voice and we'ren clearly, you, able enough to use it. you know, we know what we're talking about, to an extent, but... >> woodruff: jake, do you feel u and your friends are committed to stick with this, with this issue? >> oh, absolutely. we are comt to keep doing whatever is necessary to affect change whether it's rallies, you know, protests, whatever it takes, rally reaching out to people online. it not going to be just us that affects this change. it's going to be high schoolers allcross america who does. >> woodruff: i know you've managed to get the attion of a lot of people. jacob bennett, camille richter, thank you both.

>> thank you. e: woodruff: we now get a teacher's perspect mike conrad says the issue of school shootings has come up repeatedly in his own classroom. he tches video production at royal oak high school and joins us from detroit, michigan to discuss how educators are confronting this national tragedy. mike conrad, welcome to the program. you were able to lieten to thes two students we were speaking with. what did you make of what they had to say? >> well, i applaud them for everything they had to say. the students not only camile anb ja students around the country are taking a stand and they're using the riggeht langthey are using the right vocabulary. they a i fed up, a's time for them to help make change. so i applaud the fact tat the went to the rally today. irenjoyed hearing the thoughts, and i agree with them. >> woodruff: you were telling us that your own students are speaking up. what are they saying the shooting in florida? >> there's a lot of discussion. thussion tone has changed in the past couple of days. students are scared. i can give you an example that,

daily, just a generic.a. announcement throughout the school, when the tone goes off, the tension heightens and you hear a student gasp or a student use with fear "oh, no," beca they don't know what the announcement is going to say. that shouldn't happen in the classroom. there are students asking me how i'm prepared to defend them e into thehooter com school. it's a difficult question to answer because i can talk about all of our drills, all of our lockdowns, i can talk about everything we do as a school district and what i do in terms of my own knowledge, but, at the end of the dy, how do you prepare yourself for one of these situations that happened in florida. >> reporter:. >> woodruff: well, what is your thinking about teachers ained?armed, tr it came up just this afternoon at the white house, the president raised it with the students and teachers and parents who were -- he was meeting with. what do you think of that idea? >> i think that the moment that you put a gun on the hp of a

teacher in a classroom that we have accepted anorm that school shootings will not stop, that we are now on the front line to defend against them instead of trying to find a way toop them. i look at a classroom as a safen ronment, and i never look at it, when i say that to students or parents, that a safe environment in a classroom means defending agait shootings. i look at it as a safe place where a student can talk to me and bring their problems to me. when they come to me and tell me a student is goi to ham themselves, they trust they can say those things to me. that's a safe environment. the second i put a gun on myhi hip, i don't that relationship continues. >> woodruff: if it's not arming teachers, then what are some solutions, do you think? what's the role that teachers can play to keep students safe and themselves? >> well, i think some of it is ucation and awareness. i think that camile and jake did

a great job of explaining some of the things that have to happen prior to the point where a shooter ever walks inta school. teachers should not be a line of defense.ld the point shever get to the point where they're asked to do so. so i think we as teachers, i teach high school students, 15, 16, 17, 18-year-old students, i oould be preparing them ake the decisions to vote, to call their legislators,o march should they want to, but i think my job as a teacher is to espire and toucate, and i think that's the best thing that we can do at that point in aa classroom, note it a military zone. >> woodruff: mike conrad is a teacher at roy oak high school, in detroit. thank you very much. we turn now to a darker side of the response to the parkland loooting. hari sreenivasan es the anger, lies and conspiracy theories cropping up online.

>> our entire nation is praying for the victims and their families. >> sreenivasan: the imrediate onse to the school shooting in florida was a wave of prayers and condolences from around the country. what quickly followed? a flood of allegations and conspiracy theories about the students calling for gun reform. >> i just know we are being fed something as phony as a three dollar bill. >> sreenivasan: right-wing outlets, like gateway pundit and infowars, and online trolls are promoting the false theory that some of the parkland teens are actually paid actors. the target of many of these attacks is stoneman douglas senior david hogg. he has been called an f.b.i. plant who was coached by his father, and a "crisis actor," after video surfaced of a california cbs story featuring hogg from august. > these people saying this is absolutely disturbing. i am not an actor in any sense, way, shape or form. i was a witness to this. and live through this.ess this

e sreenivasan: many of these false accounts com extreme fringes of social media, but are now being amplified by better- known voices.te conservative wdinesh d'souza tweeted that one of the studts, interviewed by a british news program, seemed "coached." and the present's son, donald trump junior, has liked some of these conspiracy tweets. but on tuesdayflorida senator marco rubio tweeted the accusations against the students tiare: "the work of a disg group of idiots with no sense of decency." other republicans stway from conspiracy theories about coe students, instead accusing democrats and gurol advocates of using the students to push their agenda. former georgia congressman, jack kingston: >> their sorrow can very easily be high-jacked by left-win groups who have an agenda. let's ask ourselve do we really think, and i say this r sincerely, do lly think 17 year olds on their own are going

to plan a nationwide rally? >> sreenivasan: fox ne c anchor tucklson: >> all of a sudden you're seeing these kids involved in calls for very specific pieces of legislatio and the allegation is that they are in contact with orannized -gun groups. people whoave suggested that have been denounced as immoral and heartless and how dare you question these kems and attack which for the record i am certainly not doing. but i think it raises interesting qstions about how we make our law. >> sreenivasan: stoneman douglas students are pushing b against the attacks and iticisms. >> i for one just think, ignore it, firsoff. because these people are not taking action;e are. we're taking action and i don't care what a troll says. they're just hing behind a computer. we're out there on the streets. >> sreenivasan: despite all the criticisms and false accusations, the students still plan to march fogun control next month in washington and around the country. for the pbs newshour, i'm hari

sreenivasan. >> woodruff: nowthe view from a scottish town that knows the horror of gun violence first hand. many in dunblane, scotland, have pledged their support to student activists from florida and beyond. britain outlawed hand gun ownership after a massacre at dunblane primary school in 1996. the town has become frustrated by american attitudes toward gun control. s but cial correspondent malcolm brabant reports, for the first time in years, some scots see reasons for optimism.te >> rep in dunblane, a spring flower is in bloom. the snowdrop. 's especially poignant for alice dougherty. she lost 16 of her friends and a teacher in britain's deadliestin mass sho alice, a waitress in herp, mother's tea sas a tattoo immortalizing the snowdrop caaign, a parents movement which led to a nationwide ban on s.ivate ownership of handg

>> once was enough. it didn't need to happen again. >> reporter: after last week's massacre in florida, she wishes america would finally learn the lessons of dunblane. >>ou'd rather listen to the sound of guns than the sound of children lghing? is that what you're saying that their lives are no longer important? it's all about money it's all about people's right to bear arms? and i don't think people's right to bear arms is stronger than the people'sight to have an education and feel safe. and their right to hlife. >> reporter: alice's mother nora was a member of the school oversight board. three of her children were pupils. they all survived. like many in dunblane, she has become frustrated at the unending cycle of school shootings in america and the lack of action on gun ntrol. >> your first reaction is "oh, it's another one, d that's ridiculous." and those are two wrong responses to human lives being lost due to guns. but that'shat it's become. the rest of the world is looking

at america and thinking why, why are you allowing americans to shoot americans, it doesn't maks du >> reporter: alane cathedral this past weekend, the congregation prayed that americe would have a and sober reflection" on its gun laws and tat prayer would move beyond "sentiment and wora deep, growing and active resolve for change."'s th sentiment shared by mick north whose only child, sophie, was killed at s nblane. he iexasperated by america's gun laws. >> at the mome, they are plainly insane. anything that is a g has the support of the n.r.a. for being available to any citizen of the usa. i mean that is ridiculous. you have kids, teenagers being able to buy military style weapons and use them with a devastating effect we saw last week.

>> reporter: former dunblane pupil lcolm robertson is particularly aggrieved by what he sees as the failu of america's politicians to protect children. he's from a political family. his father george was britain's defense secretary and later the nato secretary general. robertson recalls thomas hamilton, the dunblane shooter, arguing with his father over a grievance, years before hamilton's anger morphed into carnage. >> i've got three children, three boys. i'm prty confident that they're safe. i mean you can never say never but i think we've done an awfuli lot incountry to make our schools much safer places and i don't go out the door with the worries that se american parents undoubtedly have today. >> reporter: here is a statistic that highlights the difference between scotland and the united states. l sast year, tland which hason a populaf 5.2 million, there were two gun related murders. if such a crime rate applied to

america, of over 320 million, there would heve been 124 murders. but according toun violence archive, the number of people killed by firearms in the united states in 2017 was nearly 16,000. that translates to every single person in dunblanewhich has 9,000 residents; plus 7,000 people elsewhere. john carnochan helped to make scotland safer. a former senior detective, he ran the pioneering violence reduction unit, which eradicated glasgow's reputation as europe's murder capal, by targeting all forms of violent behavior. >> start where you are. do what you can. and that will make a difference, you'll start to move towards it then. if we wait until we have a great gplan i suppose, it's nevng to happen. if we wait until we have some leader who rides over the hill and says we're going to fix this firearms stuff you're going to a be waitiong time. it's not going to happen. change starts at an individual level. s

that's htems change. that's how we changed it. that's what we did here in scotland. it doesn't matter where wel start, you wke a difference, and in public health terms, don't make it worse. soto think by reducing acces children to assault rifles, at's a start. >> reporter: at the tilly tearoom, the sense o frustration with america is being replaced by cautious optimier. >> i feel is a change in momentum. i watched a wonderful speech by emma gonzales, i think is her name. >> if the president wants to come up to me and telle to my face that it was a terrible tragedy and how it should ner have happened and maintains telling us that nothing is going to be done about it, i'm going to happily ask him how much money he received from the nationalifle association. >> that young person that i heard speak was the most honest, articulate speech i've heard. lt really-- i feel that there's a chance if they hold o to we said, and people get behind her, at last they can

change the corruption from the n.r.a. and the government.>> eporter: sophie north's bereaved father also feels uplifted by what he sees as the inspirational voices emerging from florida. >> keep on talking. keep using whatever means you ve to publicize your feelings on this. social media.ar i arches. even walkouts from school. make sure it stays in everllody's mind. eople how it's affected you. don't let the powers that be, divide and rule. s mae that the average american citizen knows exactly how this impacts on the average american kid. >> reporter: in dunblane, they believe the ballot box is the best way to counter ole torrent ofical donations and lobbying flowing from the gun industry. >> you change it by identifying those people you canrust in power, by electing those people you can trust in power who will make a difference. these young people who are

starting this, need to continue doing it. we need to get behind them. you that notion that never ofderestimate a small grou people can change the world because that's the way it usually happens anyway. >> ♪ children of love, cover your ears, the bad man is ♪ coming, to take away your >> reporter: eileen barr plays her song about gun violence in thmusic room of the dunbla center. it's a playground, a meeting place, a theatre, a sports hall. but above all it's a symbol ofdu nblane's rebirth and determination to live. the victims are memorialized ind engravings. there are snowdrops and other images that represent the children. sophie north's motif is her cat. generous donations from americans helped to build this place. in return dunblane offers its wisdom. >> my words to the americans uld be to just see where scotland, see where the u.k. has

come from taking those actions and just movg forward and just saying no more. >>end i would like to think could support america now in trying tchange the gun laws and make america safe. >> reporter: t view from the tearoom is one of tranquility and safety. alice dougherty is 27. that's the age her friends would have been, she has never visited america because of its gun cuure. >> we got rid of guns and there were peoplthat would havethat m. nobody walks around miserable because they don't have a gun. >> reporter: the people of dunblane are weary of being defined by tragedy, which isin rced every time there's a shooting in america.on when, theyr, will america heed the lesson of the urowdrops. for the pbs newsi'm malcolm brabant in dunblane.

>> woodruff: the trump administration confirmed last night that vice presidnce was scheduled to secretly meet top north korean officials during his recent trip to south korea. the administration said senior north korean officials pulled out ofhe meeting at the last minute, which would have come after pence sat silently in acknowledge, the northinoreans, inclkim jong-un's sister, during the olympics' opening ceremony. the trump white house considers north korea's nuclear and missile programs the top threat to ameca at the north's ability to makeri the ma required for nuclear bombs. so, how much do we know about thosprograms? >> reporter: north korea has tested nuclear weapons six times since 2006 at this mountainous site in punggye-ri.

no one from the outside has witnessed such a test, but the experts believe this propaganda movie produced by the regime offers an accurate, albeit embellished, version of what happens inside. but howuch is known about the design and size of this secret arsenal? ecjeffrey lewis is dr of the east asian nonproliferation program at the middlebury institute of international studies at monterey.es >> so black spheres are actually the estimated size of the cavities from the northr korea's nuclplosions. >> reporter: he and his team d ed terrain data gathered by satellites to bu3d computer model of the punggye-ri test site. >> we estimated where the e clear explosions had occurred. we were able to tellite photographs to see where the tunnels went into the mounniins. when we ed that, one of

mme things we realized is that that site could acate a much larger nuclear explosion than we had seen in the past. >> reporter: it led him and his team to predict the north koreans uld soon test a bomb with a few hundred-kiloton yield, much larger than their previous tests. the predicon came at the beginning of 2017. in september, seismometers detected an exosion about that big. even when testing occurs underground some gases can leak out. south korea, japan and china have surrounded the north with sensors that can detectis radioactivopes as well as so called noble gases before they decay. the ratio of noble gases xenon 131 and 133 can offer about but the north korean site is does noteem to leak very much.

>> the south koreans detected a little bit of xenon-133, but not that much and it didn't detect any other isotopes. >> reporter: physicist and former arms control inspector david albright is president of the stitute for science and international security. so not what you'd expect from a large yield weaponhey're clearly-- they're doing something and it is an ideal test site location. the explosion is sealing the material inside. >> reporter: but the north koreans do share some tidbits about what their weapons might look like, or so it seems. >> so, they've actually shown us what are presumed to be photographs of their nuclear devices and they've shown that over the last few years' time frame. >> reporter: nuclear physicist sig hecker is with the center for international security and cooperation at stanford university. he ran the los alamos national

laboratory from 1986 through 1997 and has visited north korea seven times. he believes the first weapon they tested was akin to fat man, the bomb that the us dropped on nagasaki.in t, high explosives implode a plutonium core, using an instant nuclear chain reaction or explosion. north korea's first test in 2006 was an apparent failur but in 2009, test number two was a success. since then, the yields have grown steadily larger. and that leads experts to believe the north koreans have developed a so caed boosted fission bomb. >> the boosted bomb is one where you take highly enriched uranium or plutonium and you actually put the fusion fuel inside to sort of help light more of the plutonium or highly enriched uranium.

>> reporter: in 1957, great britain tested a one stage boosted thermonuclear bomb. it's yield: 720 kilotons, or about 50 hiroshima bombs. as but the trouble with them is as you incthe yield, it gets bigger and bigger in diameter, and it uses incredible amount of weapon-grade uranium. and so, all the countries are mogevated to go to the two-s weapon. >> this is a 3d model of northth korea'monuclear weapon. they released a series of pictures and we were able to assess its size. >> reporter: a two s, ge, or hydrogmb allows for a much larger yield in a smaller, lighter package. it begins with a plutonium or highly enriched uranium explosion, stage 1, that creates enou energy to squeeze hydrogen and its isotopes, causing fuon, stage 2. the u.s. tested more than 100 hydrogen bombs ipacific. the largest was 15 megats or

15,000 kilotons, more than 1,000 hiroshima bombs. after the last north korean test, the regime released a picture of a what looks like a two stage device. >> it looks as if this last test, the yield, the explosive yield of that is large enough that in most likelihood, my view bomb which we call a two-stage bomb. >> reporter: but are these weapons small, light and robust enough to be efficiently delivered on a missile? the experts believe the north koreans have designed their bombs with all of this in mind from the outset. >> the first bomb was mostly, i think, they d to prove to themselves, essentially a proof of principle that they can actually make an efficient bomb. and from that point on, they were determined towards making that bomb deliverable. >> so, they've to spend time, i think, working on getting the yield up and not increasing the size too much, and i think that

ey've done. >> reporter: so it is likely the north koreans have bombs small enough to be delivered on short range missiles. but weapons that are mounted on medium rge or intercontinental ballistic missiles are a much bigger challenge. >> they have to be smaller. they oht to have to be lighter. they have to be more robust. >> reporter: and what about the missiles themselves? what can they deliver, and where? the rocket science in our next foport. i'm miles o'briethe pbs newshour. oo >>uff: one of the country's most significant evangelical voices, and religious leaders, of the past century died today. billy graham preached to hundreds of millions of people around the world over decades,

was a counselor to presidents, died at the age of 99. hari sreenivasan has this look back at his life. >> and god warns e mve and every woman and every boy,ou ghe of jesus christ, to prepare to meet al god! >> sreenivasan: billy graham, the evangelist who became known america's pastor," first attracted national notice in 1949 when thousands flocked toin his revival me in los angeles. nis scene was repeated ag and again over the next half century, as the faithful thronged events dubbed "crusades." >> welcome to madison square garden and the billy graham new >> sreenivasan: his were the first religious services to be televised nationally, raising millions f dollars that helped spread his brand of evangelism. billy graham was born on a dairy farm in north carolina in 1918 to presbyterian rents.

he began preaching whileid attending flbible college, and a few years later in illinois, he met his wife, ruth bell. eir marriage lasted 64 years until her death in 2007 during the tumultuous early days of the civil rights movement, graham demanded his audiences be physically integrated, once removing a rope barrier that separated the worshippers by ylor. >> when god looks he doesn't look at the outward appearance, the bible says he looks at your heart. >> sreenivasan: and, he carried his message of peace and equalimillions around the world, traveling to 185 countries. a at sydney airport, evangelist dr. billy grahamives to begin an australia-wide crusade. >> sreenivasan: overears graham ministered to popular world leaders, as well as those, reviled by much as north korea's kim il sung. a

though life-long democrat, the evangelist said he never favored one party over the other, and that gave him credibility with icboth democratic and repu presidents. >> if i said things publicly and preached to the president from unme pulpit somewhere, i'd never get another oppoy to talk to them privately. >> senivasan: in 1991 as the first gulf war got underway, graham was in the white house with president george h.w. bush and his family.er >> i turned tond i said, barbara, i said, is this the beginning of the war? and she didn't say anything, but i could sense by the way she looked that she knew something that i didn't know, that this was the beginning. >> sreenivasan: but his relationships with the powerful also drew criticism. in 2002, tapes recorded in the nixon white house revealed a conversation between graham and president nixon in which both made disparaging remarks about jewish people. graham apologized. in his later years, he said he was less concerned with political matters and more with spirituality.

millions of ordinary americans also felt personally connected with graham through his regular television appearances, as when he consoled the nation after the attacks of september eleventh. >> as a christian, i have hope, not just for this life, but for en and the life to come. there is hope for eternal life, fochrist has conquered evi and death, and hell. yes, the is hope. sreenivasan: graham continued hiscrusades, drawing thousa to his final one, in new york city, in june 2005.to >> andght i'm going to say it is great to be back in new york. >> sreenivasan: at the 2007 dedication of his library, followers, friends, family and three former presideid tribute. >> he was the first evangelisttu of any s that penetrated the iron curtain.

>> sreenivasan: in a 1992 interview on the newshour, graham tried to explain his enduring appeal. >> it took me a long time to learn that there are certain elemts true in every audienc i speak to. there's always those people who are lonely. there's a sense of guilt. and then there's also a fear of death. it's unc there. maybe, but it's and those are elements that one can touch on and speak to in the services. and i try to bring that into every sermon that i preach, that christ is the answer, he's the hope. >> sreenivasan: the revend billy graham lived out his final years at his home in montreat, north carolina outside asheville. and for more on the li billy graham and his influence, we turn to randall balmer, a historian anprofessor of religion at dartmouth college. he is the author of numerous books oncan religion, including "evangelicalism in america," d producer of the

pbs documentary, "crusade, the life of billy graham." >> tell me, what's the legacy of billy gram going to be? >> i think he will go down in history as certainly the towering religious figure of the ury. cen certainly in american religion, i suppose some people would argue that various es might contend for that, but i think he's also very imp tortant forwo reasons. first of all, he brught evangelicalism out of the shadows in the middle of the 20th century. in the early decades of the 20th century, evangelicals tewere feeling qbattered as though the larger culture had turned against them, and billy graham, beginning around 1949, 1950, begins to bring them into the public spotght and begins to make evangelicalism acceptable to larger public. part of that had to do with his

personality, the force of his personality, but part of it was that he used media quite successfully and brillialy, many ways, to bring that message to the larger public. think that the second legacy of billy graham -- and this is really quite remarkable -- that, over the course of a career that spanned more than half a century, he was never seriously charged with any scandal. it's not to say he didt misstep from time to time, he certainly did. but in comparison with other televangelists, for example, billy graham emerged with his >>tegrity and his character in tact. reenivasan: you mentioned he largely lived scandal-free. one of the few things mentioned in the obituary was the recorded conversations he had with president nixon which he later apologized for in siding with some of then ati-semitic views that the president had held. >> he did, and i think mr. graham was genuinely shocked

by this, because he had n recollection of the conversation. richard nixon had a way of kind of bringing -- pulling people into his orbit, into his dark personality in some ways.ot that'so excuse mr. graham at all. i think what he said was unforgivable, as he acknowledged, but it's one of the dark marks on his life and on his career, yes. >> sreenivasan: do you think that he was aware of how politically powerful evangelilism had become in america or has become in america? >> he was, and he was not hap about that. when the religious right emerged inhe late 1970s in opposition to desesegregation, billy graham was uneasy about it snd made several statements to the fact that he afraid that those on the far right would try to co-op evangelicalism for their political ends, and he was

not happy about that. >> sreenivasan: and you also bring out the important point that he did this barn storming and evangelizing in an area pre-youtube, you know, in an era unlike the evangelical ministert we sday who are using television and the internet to reach these wide audiences, he actually physically went to all these countries. >> he did. he was ar vey prepared evangelist but used media along the w to amplify his influence and make himself really into a religious celebrity in the 20th century.re >>ivasan: do you think that there is an heir apparent to -- is anybody doing what billy graham is ableto do or is that even possible in this era? >> i don't think so. i think there really will be only one billy graham, and say that because i think he came to prominence at a unique moment in history when there are varus new media technologies reaching

e publi radio had been aroundr several years, certainly, andhe evangelists had used radio, but graham seized on television, he seized on publication with his magazine, the hour of decision, or decision magazine, rather, and he exploited media brilliantly in order to make himself into a household name and, as i said earlier, a religious celebrity probably without peer in the 20th century. >> randall blmer, dartmouth college. thank you. >> thank you. >> woodruff: and a news update before we go: the sheriff in florida's broward county says depu rifles on school grounds throughout the county, site of the deadly shooting in parkland. and that's the newshour for tonight. i'm judy woodruff. join us online and again here tomorrow evening. u for all at the pbs newshour, thank you and see you soon.

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elyse: we're the history detectives, and wetie going to invesgate some untold storoms fr america's past. gwendolyn: home part of a modern-day wagon train gwendolyn: home halfway across the world? wes: and was abraham lincoln's signature used in one of the most notoriousys of the 20th century? elvis costello: watchin' theetectives ♪ ♪ i get so angry when the teardrops start ♪ ♪be but he can't wounded ♪ it's just like watchin' the detectives ♪