>> pelley: tonight's republican cbate takes on new urgency. it could be the last chance to catch trump before next week's super tuesday. usso tonight, elizabeth palmer takes us inside syria at a turning point in the civil war. >> reporter: there is certainly no cease-fire 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? r ans for a wide body aircraft for wide bodies. >> at the end of the day, it's kingabout making money. captioning sponsored by cbs this is the "cbs evening news" with scott pelley. >> pelley: this is our western edition. tonight, the five republican presidential candidates are holding their final debate

before super tuesday, the 12 primaries and caucuses that could be the turning point. for some it is a fight for survival, but for dominant donald trump, he is expected to draw most of the fire tonight, and now his tax returns have become an issue. major garrett is in the debate city of houston. greeeporter: 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 ohd cruz ahead, and john kasich has been leading in ohio. ht another poll put marco rubio well behind trump in his home state of florida. mpday, 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 call for trump to release his tax returns. trump then took to twitter to can 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 n'recent tax return. the caption, "isn't this ridiculous?" 2 e tax issue bedeviled romney in the 2012 campaign after democratic senate leader harry nid made a similar claim to what romney is now saying about wump. >> 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 r ter debunked. taxhis 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 e'itter that, "tax returns have zero to do with someone's net worth." romney's response, "me thinks the donald doth protest too much." trump's g.o.p. rivals marco rubio and ted cruz have both pledged to release their returns. >> they're just not very exotic, tit we will release them, sure. >> i haven't made enough money that my tax returns are not that interesting.

>> reporter: donald trump is on a three-state winning streak and won 60% of the delegates awarded so far. tuesday presents the biggest haul of all-- 595 delegates, just under half of the amount ioquired to secure the republican nomination. >> pelley: major garrett, for us tonight. major, thank you very much. the next democratic debate-- i should say primary, is saturday in south carolina. erre's nancy cordes. >> we could just turn this into a revival. >> reporter: hillary clinton's inner preacher came out today as a e courted black crowds in south carolina low country. >> i think we need more singing, don't you? i sing because i'm happy. i sing because i'm free! i reporter: in michigan, bernie sanders was focused on minorities, too, meeting with residents in water-stricken flint. c people were coming saying, "this water is brown. he're getting rashes," and they anntinued to ignore it. >> reporter: neither candidate hon win in the delegate-rich super tuesday states without minority support.

p 2008, african americans alone made up half of the democratic nectorate in alabama and nessgia, and nearly a third in virginia and tennessee. 32% of democratic voters in n xas were hispanic. >> when you have people like trump saying that mexicans are rapists or criminals, that is an eptrage. n reporter: a new national poll finds clinton leading sanders among hispanic voters by a margin of two to one. she has a similar edge with e rican americans though her fosband's crime bill has been a sticking point for some. two black lives matters protesters interrupted a clinton fund-raiser in charleston last night. >> reporter: the protesters were escorted out, and clinton later said she was sorry for some of the terms 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 particular, are handled, scott, because they say too many young blacks and latinos are ending up behind bars. >> pelley: nancy cordes. thank you, nance. a study out today confirms the methane leak that forced thousands from their homes in porter ranch, california was the largest in u.s. history. over four months, the ruptured well spewed more than 100,000 tons of methane-- almost as much pollution as 600,000 cars put out in a year. in syria, u.s.-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's rare for a reporter to get into syria, but today our elizabeth palmer covered the dictatorship's advance through an apocalyptic land. >> reporter: this used to be a

neighborhood. syw it's a battlefield. onere the syrian army says it's got the enemy on the run. there's just been an air strike behind me. we're about five miles from the annter of damascus, and the syrian army is trying to clear this suburb of opposition e-ghters. 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 wldiers, take us to see the buildings half a mile away where he says the rebels are now hiding. overhead, we can hear the helicopters scouting their target. then... ( explosion ) riat are they hitting, solmer? rrhey're terrorists," he says. those are barrel bombs? barrel bombs are basically canisters filled with explosives rolled out of a chopper. they're cheap but horribly inaccurate.

and are there any civilians left over there? fio, no," he says "only lighters," but there are nderters' families, too, cowering under the attacks. nearby, we enter tunnels the soldiers say were dug by fighters with the al qaeda- linked al-nusra front where they hid and fought for years. leneral youssuf, the man in charge, leads the way through llins he now controls. you're still using air strikes in the suburbs in order to fight nusra? "yes," he says, "because they're dangerous for syria and the world so we're justified in using any weapons that are legal." but that means that when this gaer-stretched and undertrained army does gain ground, its s ctories look like nothing

more than 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 thuce with the rebels to allow food and supplies to reach civilians. >> pelley: elizabeth palmer with rare firsthand reporting inside syria tonight. elizabeth, thank you. today, the director 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 told the court that order is dangerous. >>ff pegues has more. >> reporter: in its filing, apple says the f.b.i. is seeking s dangerous power and that it would be forced to dedicate six to 10 apple engineers to create new code that apple calls the government operating system or government o.s. enple said there would even have to be a government's forensics edb on company grounds that could be used to open hundreds of other seized devices in law enforcement's possession.

apple says: the company believes the case triggers first amendment protections, and writing computer code is equivalent to free speech. n this is the hardest question r:have seen in government. >> reporter: f.b.i. director james comey reassured members of congress today that the bureau tly wanted access to the iphone used by san bernardino terrorist saed farook. comey said the f.b.i. is standing on firm legal ground, but congress needs to set the limits on how far government vavestigators 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 as a people. >> reporter: apple agrees that congress should have a bigger role in this debate, but, scott, moe court 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 ersterday killed at least four people, including three in waverly, virginia, where we find chip reid tonight. >> man, it's an experience, man. you got to experience it to talk about it. hereeporter: 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. re reporter: but the tornado tore his neighbor's mobile home from its foundation and sent it sailing across a highway. hetwo-year-old boy, his father, and another man died. their bodies and other debris were found 300 yards away. somehow, the boy's mother survived with serious injuries. ea nearby appomattox, virginia, er a-year-old man died and 100 buildings were damaged after a funnel cloud left an eight-mile path of destruction. ro least three tornadoes were

farrted in north carolina. in oxford, parts of this farm inre leveled. in pennsylvania, a tornado ripped through amish country, hitting structures in narvon. a torrential downpour lead to shash flooding in and around washington, d.c. and left one major road flooded for the morning commute. 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 asves capsized a coast guard seat as it was trying to rescue fishermen on another vessel that lyd run aground. and back here in waverly, virginia, you're looking at a photograph of a-plus tires before the tornado. now you're looking at a-plus tires after the tornado. this was the garage door. that up there is the metal that was once the roof. scott, it's a good example of n a happens when a tornado meets a building made of sheet metal. >> pelley: and we want to point out, no one was injured in the coast guard incident today.

peip, thanks very much. the world's appetite for portable electronics has nyiggered huge demand for rechargeable batteries, but many bu these batteries are now bursting into flames in places you would least expect. vinita nair is looking into ohis. >> reporter: when the fire first ignited, employees at this thntucky gas station thought it ass a bomb. it turned out to be an e- cigarette that exploded in josh jmilton's pants. he suffered third degree burns. it's just the latest incident involving defective lithium ion batteries that power e- cigarettes. 21-year-old evan spahlinger had ve be placed in a medically induced coma for three days after one of them blew up in his mouth. a it's an alternative to smoking cigarettes. it's supposed to be a safer and shealthier way of doing it. >> reporter: the same battery cells that power e-cigarettes, also power hoverboards. since december there have been oa 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 corners. >> what we're seeing right now is a situation where maybe some me shese batteries are simply not made to the same standard as se battery that are made say, t sony or panasonic, which have much more stringent quality control. >> reporter: whitacre says that lithium-ion-powered items like e-cigarettes and hoverboards are considered high-power applications. if their batteries are badly designed when they are charged they can overheat. is it something that the user is doing incorrectly? >> no. at general, with this kind of technology, it's very difficult fr the user to be at fault. y ere is a well-controlled charging circuit, and there should be a good package that ere cell lives in. hath of those things should be gssigned to protect the user. >> reporter: industry advocates say these incidents are still hat and that users should always use compatible batteries and chargers. they say to avoid battery otntact with metal objects,

scott, such as coins, keys, or ley:lry. >> pelley: vinita nair, thank you very much. there's a plan to give wider air passengers wider seats. we'll get to the bottom of it. cod a young fan bags quite a gift from a legend when the cbs even news continues. go, go, go, go, go, go... touchdown! ♪ choir and harp music. this place, it's the best-kept secret in football since... hey, how did he get in here?! and with toe nail fungus! fight it! with jublia. jublia is a prescription medicine used to treat toenail fungus. use jublia as instructed by your doctor. now that's prime time. most common side effects include ingrown toenail, application site redness, itching, swelling, burning or stinging, blisters, and pain. you ready to fight it?

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better taste. better nutrition. better eggs. what backache? what sore wrist? what headache? advil makes pain a distant memory. nothing works faster stronger or longer what pain? advil. >> pelley: airbus has an idea >> 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 reconfigurable bench. tr could seat the traditional woree passengers, shift to two people who need additional space, including overweight enssengers, or even fit a fourth person, like two parents and two small 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 the 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 that are less awful. >> reporter: airbus previously sought patents for a design miacking passengers and this semi-standing concept. seat maker zodiac created a esxagon pattern where the middle seat faces the passengers in the aisle and window while adding up ma 30 more passengers per plane. tennessee congressman stephen cohen worries extra seats could diopardize safety making it hard to evacuate within the required 90 seconds as seen in this video. he's authored a bill requiring the f.a.a. to set minimum seat- size standards. f if people can't get out of an airplane in emergency conditions they lose their lives. it shouldn't be after there's an accident. after there's an accident, it's ido late and people are dead. >> reporter: the big question e w, scott, will an airline say

they want these seats and will safety regulators ever allow them to be installed in a plane? >> pelley: kris van cleave, thank you, kris. what's killing players in the n.b.a.? what a new study has found next. stock prices, earnings, and dividends... an equity summary score that consolidates the stock ratings of top analysts into a single score... and $7.95 online u.s. equity trades, lower than td ameritrade, schwab, and e-trade, you realize the smartest investing idea isn't just what you invest in, but who you invest with. ♪ ♪song: "that's life"

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(doorbell) what's that? a package! it's a swiffer wetjet. it almost feels like it's moving itself. this is kind of fun. that comes from my floor? eww! this is deep couch sitting. [jerry bell iii] deep couch sitting! >> pelley: heart problems account for three-quarters of sports-related deaths in young athletes. now, a new study may help save lives, and here's dr. jon lapook. >> reporter: two years ago, isaiah austin was one of the nation's top college basketball players. then, a physical before the ft ra. 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 and health is more important than a game. >> reporter: in the u.s., sports-related sudden cardiac death is highest among igsketball players. one big question is what's a normal heart size for these athletes?

to find out, dr. david engel and colleagues reviewed the heart tltrasounds of more than 500 n.b.a. players. when you first saw them, you aw tght these are big hearts. ts.se are abnormal? >> the first instinct is to say these hearts are enlarged. we're not used to seeing hearts for people that are this big. the average n.b.a. player is 6'7" and the average weight is r:2 pounds. he reporter: it turns out, like any other muscle, the heart gets pgger with exercise, although the hearts of the n.b.a. players were about 10% thicker than normal, that was not felt to be dangerous. the research establishes a baseline 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 , ath. ta reporter: in addition, they isund that the aorta, the major thtery leaving the heart, is also bigger in these athletes and knowing that will help with future diagnosis. scott, dr. engel says this is now a model for evaluating athletes in other sports.

>> pelley: jon lapook, thank you very much, jon. will, soccer's biggest star came through with heart today for his biggest fan. murtaza ahmadi, a five-year-old from afghanistan was photographed wearing a lionel messi shirt made from a plastic bag. it went viral so messi sent him an autographed shirt from argentina's national team. the bag has been retired. up next, a math teacher's formula for success against the odds. so let's start talking about your long term goals. knowing your future is about more than just you. it's how edward jones makes sense of investing. for called "squamous adnon-small cell",er previously treated with platinum-based chemotherapy, it's not every day something this big comes along.

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sea otters. now she faces jl time. the bizarre legal case. next on kpix 5 weather talent appears at wx center with generic >> 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,

okncoln high school does not look like a place that inspires greatness. ed, with gates on the windows, in a tough east l.a. tighborhood. >> today is all about making your life easier. >> reporter: but look beyond all of that, and you'll find this osn, anthony yom. is ghis 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 uevironment where kids are not shamed of asking questions. do you get it? >> reporter: his approach to tiaching goes beyond calculating the slope of a curve. yom makes his class meet after school, 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, les it worth it?" every single one of them say it was so worth it. >> reporter: for three years in a row, every student that has walked into his class has passed the a.p. calculus test.

and this year, one student, cedrick argueta, got every question right. ac his style of teaching commands respect and his personality is very likable. he gets to know his students on a personal level. >> reporter: what is the secret here? >> they know that i sincerely ?are about them, and it's prep for them. >> reporter: with love? >> yeah, with love. >> reporter: cedrick argueta and yom were both ordered by the l.a. school board and president obama invited cedrick 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 rocket 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 captioned by media access group at wgbh access.wgbh.org

getting too close to a sea otter! they're really not afraid of humans at all the act setting off a fierce in your at 6:00 a marine biologist accused of crossingle line new at 6:00. she could go to jail for getting too close to a sea otter. >> the act setting off a fierce debate among nature lovers. >> new at 6:00 the feds do a major about-face on immigration deportation. the crackdown on sanctuary city inspired by the shooting death of a young bay area woman. >> the "black lives matter" debate inside facebook. mark zuckerberg's scathing method to his staff. what he is calling malicious. >> the stash of drugs hiding inside a jigsaw puzzle. >> photographers from all around the world staked out for a glimpse of this natural wonder. >> the stars have to align. >> we go in search of the rare yosemite "firefall." good evening, i'm allen martin. >> i'm veronica de la cruz. the federal government is going

after a woman for getting too close to some sea otters. kpix 5's len ramirez tells us this case is making waves up and down the coast. >> reporter: monterey bay whale watching cruises take off every day project to bring tourists closer to nature. >> oh, my god. >> reporter: larry from indiana is just back onshore after a tour. >> it was very worthwhile. we seen one breach up close. and we seen several out in the distance. >> reporter: the owner of this tour company is accused of getting too close twice. this marine biologist nancy black was already on probation for feeding orcas when she was photographed violating her probation by being too close to two sea otters. she said she was checking the health of pups but she could be the first person jailed for getting too close to sea otters. >> sea otters just