catch trump before next week's super tuesday. also tonight, elizabeth palmer takes us inside syria at a turning point in the civil war. >> reporter: there is certaiaiy no cease-firir here at the moment, and there's not going to be any time soon. >> pelley: daylight reveals the destruction done by a night of violent storms. and will this idea take off? plans for a widebody aircraft for wide bodies. >> at the end of the day, it's all abououmaking money. this is the "cbs evening news" with scott pelley. >> pelley: tonight, the five candidates are holding their final debate before super tuesday, the 12 primaries and caucuses that could be the turning point. for somomit is a fight for survival, but for dominant dona trump, he is expected to draw most of the fire tonight, and now his tax returns have becoco an issue.

city of houston. major? >> reporter: scott, republicans here all agree-- tonight could be one of the last chances to slow donald trump's momentum before key contests in his republican rivals' home state. a new poll here in texas shows ted cruz ahead, a john kasich has been leading in ohio. but another poll put marco rubio well behind trump in his home state of florida. today, trump focused on a different republican candidate, one from four years ago. the feud between mitt romney and donald trump started yesterday when romney repeated his c cl for trump to release his tax turns. trump then took to twitter to call romney one of the worst g.o.p. candidates ever and a dope. trump also tweeted a picture of himself signing what he said was a recent tax return. the caption, "isn't this ridicuus?" the tax issue bedeviled romney in the 2012 campaign after

reid made a similar claim to what romney is now saying about trump. >> the word's out that he hasn't paid any taxes for 10 years. let him prove that he has paid taxes, because he hasn't. >> reporter: the accusation was later debunked. for his part, trump has boasted he tries to keep his tax bill low. >> i fight like hell not to pay taxes. i hate the way the government spends my money. >> reporter: and he noted on twitter that, "tax returns have zero to do with someone's net worth." romney's response, "me thinks much." trump's g.o.p. rivals marco rubio and ted cruz have both pledged to release their returns. >> they're not very exotic, but we will release them. >> i haven't made enough money that my tax returns are interesting. >> reporter: donald trump is on a three-state winning street and won0% of the delegates awarded so far. tuesday presents the biggest

just under half of the amount required to secure the republican nomination. > pelley: the next democratic debate-- i should say primary, is saturday in south carolina. here's nancy cordes. >> we could just turn this into a revival. >> reporter: hillary clinton's inner preacher came out today as he courted black crowds in south carolina low country. >> i think we need more singing, don't you? i sing becausu i'm happy. i sing because i'm free! >> reporter: in michigan, bernie sanders was focused on minorities, too, meeting with residents in water-stricken flint. >> people were coming saying, this, water is brown. we're getting rashes," and they continued to ignore it. >> reporter: neither candidate can win in the delegate-rich super tuesday states without minority support. in 2008, african americans alone made up half of the democratic electorate in alabama and georgia, and nearly a third in virgininnd tennessee. 32% of dememratic voters in texas were hispanic.

trump saying that mexicans are rapists or criminals, that is an outrage. >> reporter: a new national poll finds clinton leading sanders among hispanic voters by a margin of two to one. she has a s silar wedge africann americans though her husband's crime bill has been a sticking point for some. two black lives matters protesters interrupted a clinton fund-raiser in charlestown last night. >> well, can i talk? i say. >> reporter: the protesters were escorted out, and clinton later said she was sorry for some of theeerms she used in the 90s, including the use of the phrase "super predators." she was using the term to describe violent young gang members, but now, 20 years later, says it was a poor choice of words. both clinton and sanders want to reform the way drug crimes, in particulararare handled, scott,

blacks and latino are ending up behind bars. >> pelley: this evening, president obama claimed progress against the isis terrorist group in syria. he said that isis has lost 40% of its territory, cut the pay of its troops, and is reduced to using civilians as human shields. but the wider warar in syria is not going mr. obama's way. american-backed rebels are on the run. the forces of the assad dictatorship are advancing for the first time in years because of russian air support and iranian troops. it is rare fair reporter to get into syria, but our elizabetet palmer covered the dictatotos advance today through an apocalyptic land. >> reporter: this used to be a neighborhood. now it's a battlefield. where the syrian army says it's got the enemy on the run. behind me. we're about five miles from the

syrian army is trying to clear this suburb of opposition fighters. there is certainly no cease-fire here at the moment and there's not going to be at any time soon. solmer, one of the syrian soldiers, takes take us to see the buildings half a mile away where he says the rebels arere now hiding. overhead, we can hear the helicopters scouting their target. then... ( explosion ) what are they hitting, solmer? >> they're terrorists, he says. those are barrel bombs? barrel broms basically canisters filled with explosives rold out of a chopper. they're cheap but hcrribly inaccurate. and are there any civilians left over there? "no, no," he says "only fighters, but there are fighters' families, too, cowering under the attacks.

soldiers say were dug by fighters with the al qaeda-linked al-nusra front where they hit hid and fought for years. general youssuf, the man in charge, leads the way through ruins he now controls. you're still using air strike nghtz suburbs in order to fight nusra? "yes," he says, "because they're dangerous for syria and the world so we're justified in use anything weapons that are legal." but that means that when this over-stretched and undertrained army does gain ground, its victories look like nothing marine few blocks of rubble. but the truth is, scott, that by now, all sides in this war are completely exhausted, and unlikely as it sounds, just a couple of suburbs over, the army has actually reached a mini truce with the rebels to allow food and supplies to reach civilians. >> pelley: elizabeth palmer with rare firsthand reporting

elizabeth, thank you. today, the direcr of the f.b.i. said that his battle with apple is the toughest fight he's faced in government. a federal magistrate ordered apple to unlock the iphone of one of the san bernardino terrorists, but today, apple dangerous. jeff pegues has more. >> reporter: in its filing, apple says the f.b.i. is seek a dangerous power and that it would be forcedo dedicate six to 10 apple engineers to create new code that apple callses the government operating system or government o.s. apple said there would even have to be a government forensic lab on company ground that could be used to open hundreds of other seized diswies dwooises in law law enforcement's possession. apple says: the company believes the case triggers first amendment

computer code is equivalent to free speech. >> this is the hardest question i have seen in government. >> reporter: f.b.i. director james comey reassured members of congress today that the bureau only wanted access to the iphone used by san bernardino terrorist syed farook. comey said the f.b.i. is stand on firm legal ground, but congress needs to set the limits investigators can go. >> i'm a huge fan of privacy. i love encryption. it's a great thing. but our need for public safety and our need for privacy are crashing into each other, and we've got to sort that out a aa people. >> reporter: apple agrees that congress should have a bigger role in this debate,, but, scott, the courtt case is moving forward. google and facebook are expected to file legal papers in support of apple. >> pelley: jeff pegues for us tonight. jeff, thank you. tornadoes in several states yesterday killed at least four people, including three in waverly, virginia, where we find

>> man. >> reporter: vincent donald was about to sit down right here to watch tv when the tornado slammed into his mobile home, sheering off the roof and the wall. do you feel lucky to be alive? >> i'm not lucky. i'm blessed. >> reporter: but the tornado tore his neighbor's mobile home from its foundation and sent it sailing across a highway. a two-year-old boy, his father, and another man died. their bodies and were dewe were found 300 yards away. somehow, the boy's mother survived with serious injuries. in nearby appomattox, virginia, a 78-year-old man died and 100 buildings were damaged after a funnel cloud left an eight-milil path of destruction. at least t tee tornadoes were reported in north carolina. in ox fard, parts of this farm were leveled. in pennsylvania, a tornado ripped through amish country,

a torrential downpour lead to ash flooding in and around washinon, d.c. in the new york area, a gust of wind sent this truck airborne. and, scott, take a look at this. off queens, new york, 12-foot waves capsized a coast guard boat as it was trying to rescue fishermen on another vessel that had run aground. and backere in waverly, virginia, you're looking at a photograph of a-plus tires before the tornado. now you're look at a-plus tires after the tornado. this was theiage door. that up there is the metal that was once the roof. scott, it's a good example of what happens when a tornado meets a building madad of sheet metal. >> pelley: and we want to pointut, no one was injured in the coast guard incident today. chip, thanks very much. the world's appetite for portable eleronics has triggered huge demand for rechargeable batters, but many of these batteries are now

you would least expect. this. >eporter: when t te fire first ignited, employee as this kentucky gas station thought it was a bomb. it turned out to be an e-cigarette that exploded in josh hamilton's pants. he suffered third degree burns. it's just the latest incident involving defective lithium ion e-cigarettes. 21-year-old evan spahlinger had to be placeddn a medically induced coma for three days mouth. >> it's an alternative to smoking cigarettes. it's supposed to be a safer and a healthier way of doing it. >> reporter: the same battery cells that power e-cigarettes, also power hoverboards. since december there have been 52 reported incidents involving hoverboards catching on fire. jay whitacre is a professor at carnegie mellon university. he said the demand to make these products cheaper and more powerful has led some companies to cut cornerrers. >> what we're seeing right now is a situation where may be of

made to the same standard as the battery that are made say, at sony or panasonic, which have control. >> reporter: he says lithion-ion-powered items are applications. if their batteries are badly designed when they are charged they can overheat. is it something that the user is >> no. in general, with this kind of technology, it's very difficult for the user to be at fault. there is a well-controlled charging circuit, and there should be a good package that the cell lives in. both of those things should be designed to protect the user. >> reporter: industry advocates say these incidents are still rare and that users should always use compatible batteries and chargers. they say to avoid battery contact with metal objects, scott, such as coins, keys, or jewelry. >> pelley: vinita nair, thank you very much. there's a plan to give wider air passengerrers wider seats.

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what pain? advil. >> pelley: airbus has an idea that could revolutionize the in-flight experience. think flying station wagon. here's kris van cleave. >> reporter: jet maker airbus wants to patent a seating concept taking a row of three airline seats and turning it into a rapidly and easily reconfigerable bench. it could seat the traditional three passengers, shift to two people who need dcialg space, including overweight passengers, or even fit a fourth person, children. >> the airlines will consider anything that allows them to make a buck. >> reporter: ben mutzabaugh is the editor of "usa today's" "today in thee sky" blog. >> if we've seen nothing else in the airline industry, they're very clever about coming up with ways to sell seats to passengers, especially when they can charge more for either seats that are better or for seats

>> reporter: airbus previously sought patents for a design stacking passengers and this semistanding concept. seat maker zodiac created a hexagon pattern where the middle seat faces the passengers in the eye and window. tennessee congressman stephen cohen worries extra seats could jeopardizize safety making it hard to evacuate in the required 90 seconds as seen in this video. he's author add a bill ruiring the f.a.a. to set minimum seat-size standards. >> if people can't get out of an airplane in emergency conditions they lose their lives. it shouldn't be afternoon an accident. after an accident, it's too late and people are dead. >> reporter: the big question now, scott, will an airline say they want these seats and will safety regulatoror ever allow thth to be installed in a plane? >> pelley: kris van cleave, thank you, chris.

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>> pelley: heart problems account for three-quarters of sports-related deaths in young athletes. now, a new study may help save lilis, and here's dr. jon lapook. >> r rorter: two years ago isaiah austin was one of the nation's top college basketball players. then, a physical before the n.b.a. draft revealed a heart problem, ending his career. >> i just didn't know what to do with it, but it was just-- you know, just accepting it, accepting that life is in-- and health is more important than a game. >> reporter: in the u.s., sports-related s sden cardiacc death is highest among basketball players. one big question is what's a normal heart size for these athletes? find out, dr. aaron lane-davies and colleagues reviewed the heart ultrasounds of more than 500 n.b.a. players. when you first saw them, you thought these are big hearts. these are abnormal? the first instinct is to say these hearts are enlong-ranged.

for people that are this big. the average n.b.a. player is 6'7" and the average weight is 222 pounds. >> reporter: it turns out, likeke any other muscle, the heart gets bigger with exercise, although the hearts of the n.b.a. players were abouou 10% thicker than normal, that was not felt to be dangerous. the research establishaisee seline for doctors going forward. and how does this help us? >> this should help us distinguish those changes from dangerous heart conditions that can lead to sudden cardiac death. >> reporter: in addition, they found that the aorta, the major artery leaving the heart, is also bigger in these athletes and knowing that will help with future d dagnosis. sct, dr. engel says this is now a model for evaluating athletes in other sports. >> pelley: jon lapook, thank you very much, jon. well, soccer's biggest star came through with heart today for his

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>> pelley: we end tonight with a solution to a math problem that has stumped the best minds for centuries. how do you get school kids to succeed at calculus? here's mireya villarreal. >> reporter: from the outside, lincoln high school does not look like a place that inspires greatness. old, with gates on the windows, in a tough east l.a. neighborhood. >> today is all about making your life easisi. >> reportete but look beyond all of that, and you'll find

>> this is almost similar to this guy right here, right? >> reporter: the son of korean immigrants, yom teaches what is considered the hardest class in school, advanced placement calculus. >> one of my strategies, really to make sure to provide that environment where kids are not shamed of asking questions. do you get it? >> reporter: his approach to teaching goes beyond calculating the slope of a curve. yom makes his class meet after schools, on weekends, and even holidays. the hard work has paid off. >> it's not always fun, but i do know for sure, once they get the score and if i ask them, "hey, was it worth it?" every single one of them say it was so worth it. >> repepter: for three years in a row, every student that has walked into hislass has passed the a.p. calculus tt. and this year, one student, cedrick argueta, got every question right. >> his style of teaching commands respect and his personality is very likable. he gets ton his students on a personal level. >> reporter: what is the secret here?

care aboututhem, and it's prep for th. reporter: with love? >> yeah, with love. >> reporter: cedrick argueta and yom were both ordered by the l.a. school board and president obama invited seg sed rick to the white house science fair. the 17-year-old wants to go to cal-tech and become a rocket scientist, while yom's focus is on his next batch of calculus students. >> this is not rocketet science. >> reporter: mireya villarreal, cbs news, los angeles. >> pelley: and that's the cbs evening news for tonight. for all of us at cbs news all around the world, good night. captioning sponsored by cbs

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