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>> tonight, on the bus and behind the scenes with ted cruz as the gloves comeor president. >> he's got this cloud over his head. >> donald trump now taking aim at a serious threat in iowa and new hampshire. >> cruz appealing to thers -- >> you had me at hello. >> -- and impersonations. >> make sure to hang him high. into the ice. we go deep inside a the view is stunning. but what we see is sobering. the effects of warmer temps up close. this mammoth glacier in icelandrming rates. what this means for the ocean beaches here at home. and millions dreaming of millions tonight as the powerball jackpot nrritory. a last-minute surge of ticket buying has pushed the jackpot to half a billion dollars.cky tonight.

good evening. thanks for joining us. we begin with the shocking claim from north korea that it tested a hydrogen bomb. scrambling, and the u.s. launched planes to verify. but out on the campaign trail it gave candidates a chance to appear presidential.

behind the scenes on aour with one of the gop front-runners, ted cruz. abc's tom llamas has the story.ht an alarming claim from north korea. state television announcing they had successfully tested a bomb to protect north korea from warmongers like the u.s. for hours after, the world waited nervously. but finally, after analyzing the shock ouse calming fears. >> the initial analysis is not consistent with the claims that the regime has made of a bomb test. >> reporter: today on the campaign trail the candidates weighing in. >> north korea is a paranoid, isolated nation.have a hydrogen bomb, if that's true, you are a threat. >> this underscores the gravity of the threats we are facing right pent the day with republican candidate senator ted cruz. >> i thank you.

the caucuses are just 26 daysow are you doing? >> reporter: ted cruz has spent a lot of time and resources here. >> welcome to iowa. >> reporter: and the polling is in his favor.eck and neck. far ahead. with rubio trailing at 14% and carson at 10%. but some republicans worry cruz is too unwilling to compromise with congress, to win the general election. >> how can you be a president and hate the democrats and hate the culture of washingtonive? >> i don't hate the democrats. it's hillary clinton who describes her, quote, enemies as republicans, as halfonsiders her >> i'm praying for you. >> thank you very much. >> reporter: his supporters coming out in droves.ears when they meet him. >> you got emotional speaking to senator ted cruz. you're still emotional. why are you crying? >> because we need such a changeur country. >> reporter: he's on a six-day, 28-stop tour of iowa in an effort to secure every corner of

>> talk to me in iowa. >> we spend a lot of time just one on one asking for the voters' support. people expect to look you in the eyes. there's an old joke in iowa, are you voting for so and so for no, no, i couldn't possibly. i've only met him five times. >> reporter: but nationally the landscape is different. trump trumps the competition. cruz is just at campaign stop a cruz supporter wanted answers. >> how are you going to convince independents and democrats to support you when we know the numbers are against us >> i think the way we do it is as reagan said in 1980. you paint in bold colors, not paleter: getting close to trump in the polls doesn't come easy or without a fight. on television and in newspapers trump questioning if senator cruz can even be president since canada to an american mother. trump even suggesting democrats would have a field day challenging cruz's presidentialhe gets the nomination.

democrat, whoever it may be, and you have this hanging over your head if they bring a lawsuit? atwo, three years -- >> he says he's a naturally born citizen because his mother was u.s. born, a u.s. citizen, and as a result he's a natural-born citizen. >> well, i hope he's rioments after stepping off his campaign bus this morning, cruz put it to rest. >> the child of a u.s. citizen born abroad is a >> reporter: donald trump a couple weeks ago talked about your ethnicity and your religion. now he's talking about, you know, that you were born in canada. not criticizing it but sayinge problems with that. why do you think he's doing that? >> oh, look, i'm not going to try to psychoanalyze donald trump. you know, my view, ifu think he sees you as a threat? >> you'd have to ask him that. a lot of folks in the media would love to see donald and me get in a giant food fight. and i'me gauge in that. i hope donald won't either. >> reporter: if i'm a trump supporter in iowa or anywhere else in the country, why vote for ted cruz? >> well, listen, ird is stronger than his.

than every other republican candidate running. >> reporter: cruz and trum have certainly played nice so far, even seemed to agree on one issues of the campaign season, immigration. what do you do with the 11 million undocumented immigrants in the u.s.? deport them? or they stay here? >> you enforce the law. you we will secure the borders. we'll build a wall. we will triple the border patrol. we'll increase fourfold the fixed wing and rotary wing we will end sanctuary cities. we'll put in place a strongly verified system at the workplace. we will end welfare benefits for those here we can solve this problem. >> reporter: tonight on cnn trump saying cruz's immigration plan sounds very familiar. >> he said and we will build a wall. so now he's taking my idea for the wall.aking it. i think it's the right thing to do. >> reporter: so how is cruz catching up to the trump train? one of the cornerstones of cruz's support here in iowa anduntry is his faith. >> we need those prayers desperately. >> reporter: cruz is also trying

a fitbit. >> do you go up and down steps? that is awesome. >> reporter: and making voters laugh with comedy bits like his tonight in iowa it was jerry maguire. >> you had me at hello. >> reporter: monday it was clint ea hang him high. >> bye-bye. have fun storming the white house. >> reporter: he also does a mean billy crystal. >> you look marvelous. >> not bad. 45-year-old republican candidate graduated from princeton, then harvard law, near the top of his class. a champion debater and an actor on t helped him deliver his message to washington with a twist. >> i do not like green eggs and ham. i do not like them, samter: the night cruz announced he was running for president last more -- >> i believe in the power of millions ofervatives rising up. >> reporter: his cuban immigrant father waited backstage.

>> reporter: cruz met his now wife heidi while trail for george w. bush's 2000 white house run. married nearly 15 years, they have two young nd catherine. >> it's really been a joy to get out to the states and just meet with thousands and thousands of people who share our values and turning out to hear the message of ted cruz. >> reporter: he admits it's hard being away from his family and tries to bring his girls on the road when he can. >> what's it like to beghters when they're so young? >> it's the hardest part of the campaign. i mean, our girls, caroline is 7, catherine's 5. we try toe road as much as we can. they're coming out. they'll be joining us here in iowa on friday. what they're on the bounce they're bouncing off the ith it. my 5-year-old catherine two days ago woke me up in my hotel room my ipad ringing thatwas face-timing me from her ipad. >> is it tough you? don't get that time back.

it. i couldn't look my daughters in the eyes, if i had the ability to do something to stop it, to bring america back and i didn't stand up and lead. so that's a very big part of why i'm a shining city on a hill. >> reporter: tonight cruz working late into the evening, making convince republican voters to put their faith in him. [ applause ] for "nightline" tom llamas in storm lake, iowa. up-close look at the impact of global warming from deep inside a glacier. and later, the huge t that has so many americans hoping to wake up millionaires. to severe crohn's disease is tough, but i've managed. except that managing my symptoms was all i was doing. my doctor, he said humira is for adults like me who have tried other medications but still experience the symptomsere crohn's disease. and that in clinical studies, the majority of patients

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you know, when you think of the word "breathtaking," the location of our next story comes to mind. iceland. the land of fire and ice. butting faster than ever. it's a massive undertaking live on "gma" taking us deep inside a glacier, where you cannge happening up close. abc's amy robach has the story. >> oh, my gosh. >> reporter: we brought. we're just getting inside that crater. the first ever live drone camera over an active volcano. now we're bringing you imidating standing here looking up. >> reporter: the immense forbidding ice sheets of iceland. home to a hidden worldice caves,

dangerous crevices constantly changing. this smugmug the stunning beauty and treachery of the terrain. we're standing in the middle of the melting vaknad scattered all throughout this glacier are massive vertical sinkholes that are treacherous. they go hundreds, even thousands of feet into the earth, where ice is melting faster and water levels in the atlantic rise even more. >> throughout geelogic time and certainly for the last 2 million years, we've gone throughriods, and glaciers come and go over time. what we're seeing right now, though-s a real rapid increase in the rate of thinning and melting that we's related to human-induced climate change. >> reporter: gearing up for this treacherous journey has been a multiday expedition. just callse guys glacial life savers.

of enced ice climbers. and true masters of this forbidding terrain. they train on icescapes like escend into the depths of the coldest climates, braving perilous weather conditions to reach people trapped in the most intimidating of the ice, they've canceled hollywood too. keeping crews safe on blockbusters from "star wars" to "game of thrones." we joined them right in the heart of this icy wonderland. >> walk up that wall of ice. and it's perfectly safe? >> >> you hesitated. >> reporter: ready to lock and load. it's my turn to attack the slippery slope.ing myself up by my own weight, picks on my hands and feet, the ice giving way beneath me. getting a small taste of how difficult, dangerous, and

>> i got up. whoo!ar and foot our team trekking nearly a mile through water, rocks, and ice, all in arctic temperatures. the landscape,ous. and disappearing fast. losing an average of 11 billion tons of ice per satellite picture taken in later. iceland is melting, and that water has to go somewhere. >> when you're talkingea level, you're talking about impacting the tremendous population around the world. >> reporter: including miami's coastline. those waters already climbing an inch a take a look at this. if sea levels keep rising, in two centuries some scientists warn that city could be completely underwater. even new york.

around the globe, entire ways of life now threatened. so we're plung surface of the ice in a never-before-attempted live event. >> hey, guys. go for it. go ahead and start ice orter: going deep into this glacier. passing bands of darker ice like the rings of a trees showing ash and debris from volcanicm ages past. vakna, a glacial sinkhole, a massive pipe for be thousands of feet deep. and all this melting ice eventually ending up in the ocean. >> this is remarkable watching them scale this massive ice wall. its skill, but it's all to get to the bottom. what do you expect they'll see when they get down there and what will we all see? >> this is one of the most interesting and least known parts of glacier is how does water from the surface get to the base and help lubricate the base to make the glacier flow faster? >> reporter: it's aay down but finally --

you. this is amy again pu made it to the bottom? >> that's right. >> tell me what you're seeing. looking at. >> everything is awesome. >> he went ahead with -- >> i'm surrounded byice. and i can tell you one thing. i have a challenging climb in front of me. >> reporter: but not nearly as challenging as the problem we face slowing t of this vital hidden world. amy robach in iceland. up next what you could do if you win the massive powerball many trips around the world could you afford? >> announcer: abc news "nightline." brought to you by viagra. there's something in the air. the thing: about half of men over 40 have some degree of erectile dysfunction.

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tonight, the next drawing is saturday, when the grand prize is estimated to be worth $675 the largest jackpot ever. for "nightline" kayna whitworth, abc news, new york. >> of course if you win you could tweeted me abc because i have a few other ideas on how you can spend that money. thanks for watching abc news. "world news now" is coming up soon with overnight breaking news. tune in toa" tomorrow and as always we're online at abcnews.com.