this is "nightline." >> tonight, presidential candidates hitting below the belt. >> maybe make sure his pants weren't wet, i don't know. >> rubio! >> this war of words on the eve of a big vote for the democrats. >> how do you keep your energy level up? >> because i'm young, not old like you. >> we're behind the scenes with bernie sanders. will these crowds be enough to edge out the odds-on favorite in south carolina? journey to the oscars. brie larson's breakthrough role in "room." >> i want a different story! >> no, this is the story that you get! >> nominated for best actress. how playing in young mother echoed her own childhood. >>py my mom couldn't afford a happy meal. >> first the "nightline 5." i'm here with advice from

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seconds. good evening. thank you for joining us. tonight the campaign whirlwind. some unexpected twists for republicans in the already unconventional primary season. for democrats the rising tide for the outsider candidate. will this wave of support be enough for bernie sanders to win south carolina tomorrow? our david wright spent one-on-one time today probing for secrets from sanders. >> reporter: orange berg bark. home of the panthers and the lady panthers.

bernie sanders. >> you have the right to vote, end of discussion. >> reporter: we're with him backstage. >> how do you keep your energy level up? >> bus i'm young, i'm not old like you. running all over the country. we're doing great. these kinds of events really energize me, tell you the truth. >> reporter: down to the wire in the 2016 race for the white house. the primary season quickly coming to a crescendo. especially over on the republican side. >> marco rubio is a lightweight. >> he's not a strong guy. >> reporter: perhaps the biggest development today, a major endorsement. >> the best person to beat hillary clinton in november on that stage last night is undoubtedly donald trump. and so i am thrilled to be here this morning to lend my support. >> reporter: new jersey governor chris christie endorsed donald trump. >> he's rewriting the playbook of american politics because he's providing strong leadership that's not dependent upon the status quo. >> reporter: that after a

at the tenth gop debate. >> donald, relax. >> i'm relaxed. you're the basket case. go ahead. >> donald -- >> don't get nervous. >> marco -- >> go ahead. i promise you -- >> reporter: ted cruz and marco rubio tag teamed donald trump. last-ditch effort to stop him. >> gentlemen, gentlemen -- >> reporter: today at their separate campaign events, the schoolyard brawl continued. with rubio calling trump a con artist. >> it's time to pull his mask off so that people can see what we are dealing with here. >> reporter: trump calling rubio a choke artist. >> once a choker, always a choker. and that was one of the epic meltdowns. he didn't know where he was. i thought he was going to die. >> reporter: today donald trump mocked that moment during rubio's state of the union response to the president's state of the union. >> it's rubio! >> reporter: today trump splashed water around as though it were flop sweat from rubio.

trump may have peed his pants during last night's debate. >> during two of the breaks he went backstage, he was having a meltdown. then he asked for a full-length mirror. i don't know, why the podium goes up to here. he wanted a full-length mirror. maybe to make sure his pants weren't wet, i don't know. >> reporter: compared to that -- >> tearing people down is easy. building them up is what we need to be doing together. >> reporter: the democratic side seems downright tame. >> it feels like this time next week we could know who the nominees are. >> i think probably not, actually. >> let's assume you run the table and you're the democratic nominee. trump's the republican nominee -- >> that would be a lot of fun. >> how do you take him on? >> a man whose ideas and posture and behavior so is divisive, which really becomes an embarrassment to the united states of america. i don't think that's going to be a tough race. >> reporter: both of them are drawing huge crowds, including many first-time voters. both rail against a political

and sold by special interests. >> we the people are going to have a government that represents all of us, not just a handful of billionaires. >> reporter: one rails against billionaires. the other insists his billions are what allow him to be his own man. >> i know the best people and i'm totally self-funding my campaign. >> in an odd way you guys are flip sides of the same coin. >> no, i don't think so. >> talking about a broken system. tapping into people's frustration -- >> no, one of us is tapping into hatred. one of us is tapping into a very positive agenda. >> imagining the day when you're on that stage with donald trump what do you say to him, what's your strategy for taking him down? >> why would i tell you? he's probably watching your show. >> reporter: this is sanders' penultimate stop in the palmetto state and truth be told it's a disappointing crowd. abc's mary alice parks is traveling with the sanders

>> this is probably one of the smallest bernie sanders events i've been to. >> is it your sense he's written south carolina off? >> it's a state they'd rather have in the rear-view mirror. >> reporter: sanders is putting in his time, but mostly he's put his focus on the states voting on tuesday and beyond. in orangeberg the two democrats almost ran into each other. the orangeburg fish fry and oyster bake, hillary clinton's inside right now. bernie's waiting, he's on next. inside -- fancy running into you here. >> reporter: all the reporters traveling with the clnlinton campaign. >> i've been to all the early states with her, this is clinton country, people like her here. >> reporter: in south carolina, the democratic electorate is more than 50% black. >> we need you. >> yes, i'll be there for you. >> reporter: bill and hillary clinton have been canvassing the state making 22 stops here this past week alone. sanders has made a handful. sanders has sought inroads in the black community.

>> reporter: including a new endorsement and radio ad from director spike lee. >> when bernie gets in the white house, he will do the right thing. >> i'm hillary clinton and i approve this message. >> reporter: clinton has plenty of celebrity endorsements too, including two ads from one of the most celebrated voices in america. actor morgan freeman -- >> she understands that our country can't reach its potential unless we all do. >> reporter: last week voters at this barbershop told us they'll make up their own minds. >> that's just like politicians go to our churches when it's election time but we don't see them no other time. again, you're going to have the uneducated that's going to fall for it. those of us who pay attention, that's not working. that actually salts us, makes us not want to be in your camp. >> are you only saying that because you want our vote? or are you really sincere? the real question is will we ever really know? >> reporter: clinton and sanders have almost the same number of pledge delegates.

>> reporter: it looks like she's about to get a big boost here in south carolina. clinton also has a massive lead among so-called superdelegates. party grandees who get a say at the convention regardless of the outcomes of the primaries. >> the political establishment supports hillary clinton, end of discussion. if we do well and we start winning a whole lot of states and if the polls continue to show that i am a stronger candidate, i think a lot of these superdelegates think, maybe i'm not crazy about bernie sanders, but what is most important to us is defeating the republican candidate. >> donald trump! >> reporter: barring a big surprise tuesday night on the republican night, it's looking more and more likely that the gop candidate will be a certain brash new york billionaire. the republican race seems like it's beginning to wrap up. the democratic race, a lot of people are expecting it to as well. but bernie sanders says he's not going anywhere, he's in this

he insists he sees a pathway to the democratic nomination. >> what we're trying to do is literally unprecedented. it will be one of the great political upsets in american history. do i think we have a path to victory? i do. >> are you in this all the way up to the convention? >> absolutely, no, no. california obviously is 20% of the delegates from california, 20%. >> you're not going anywhere? >> we're going to california! we're off to the west coast, absolutely. >> reporter: win or lose big tomorrow, he's settling in for the long haul. i'm david wright for "nightline" in orangeburg, south carolina. next, brie larson is the new a-lister in the spotlight. tonight, why her role in "room" was so personal. later, he hosted the oscars before. but will chris rock confront the oscar so white controversy? to get 0% financing for 60 months on a ford suv. that's right. just announced.

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brie larson has been a successful supporting player in tv and film for two decades but spot. her breakthrough role in "room" earning her an oscar nomination for best actress. why her turn as ma gave closure to a very difficult chapter in her life. here's abc's robin roberts. >> reporter: in the intensely powerful film "room" a young mother is held captive with her 5-year-old son in a garden shed. >> stretch. >> reporter: it's the only world her son has ever known. the mother is played by a remarkable young actress named brie larson whose career has been forever changed with this performance.

it's so big you wouldn't even believe it. and room is just one stinking part of it. >> room's not stinky! i don't believe in your stinky world! >> reporter: as a young girl brie moved to los angeles with her newly single mother. and they shared a cramped studio apartment. brie would draw upon her mom's experience for her character in "room." a young mother fiercely protecting her child. >> what i forgot up until recently was waking up in the middle of the night with me and my sister and my mom all in the same bed. hearing my mom like covering her mouth, sobbing, trying to not make a sound for us to hear. it wasn't until i was prepping "room" where i realized that moment was the crack. thinking, my kids are asleep, i

where else is she going to go? my mom was struggling being in a very small space with two children and being sure to not put any of it on us. you realize how hard she tried. and you see it from this perspective that you couldn't as a kid. we lived in a studio apartment, a room with a bed that came out of the wall. my mom couldn't afford even a happy meal. we ate top ramen. i had no toys. and i had like two shirts and a pair of jeans. and that was it. but i had my mom all to myself. and i remember it being the coolest period of time. i was really, really shy. painfullily shy. so the idea of me wanting to do something that's extremely extroverted just seemed bizarre and unnatural.

you're given mostly "no." there's these sayings, just keep on going, it's around the corner! i was like, this is the longest block ever. it's like 20 years walking on one block, waiting for the corner to turn. >> reporter: while successful as a supporting player in both tv and film, brie was searchinging for that role that would show her true talents. and then she read the screenplay for a small independent film called "room." and something inside her clicked. >> good morning, wardrobe. good morning, tv. good morning, sink. >> you're 5 now? you're 5 and you're old enough to understand what the world is. you have to understand. you have to understand. we can't keep living like this. you need to help me. >> reporter: the character allowed her to create an homage to her own mother and to connect more deeply with her costar. >> this is a mothering role.

of companionship with this boy. how could you not want to just give everything you have to that brilliant little kid? he's the best. i felt so much responsibility. i knew from being an actor at the same age jake was and how badly i really wanted to be respected and i wanted to do a good job. and i saw that in jake right away. i knew that he was in it for real. i understood that he wanted to be respected and so i was always going to make sure that he felt like a creative force. >> you saved me. >> are you better now? >> yeah, i'm starting to be. >> "room" was really making it all about him. making it about his experience. and it allowed me to really feel mom in a deeper way.

i always saw it as what's on the page. it's a mom giving up her son. she thinks that he's going to be okay but she's going to die. i always assumed it was about that. when we started doing it and i would remember just holing on to jacob in that rug and i felt this just like gut-wrenching feeling of not wanting it to go -- and i realized that was me letting go of a 7-year-old. that's me letting go of my inner child. and letting go of that girl and not knowing if i'm going to get it back. >> reporter: brie's breakthrough resulted in the most powerful performance of her career. and gave her closure with the little girl she used to be. >> it's such a powerful metaphor for me now. it trips me out that this movie is the thing that's giving me that experience. >> i'll say bye-bye to room.

7-year-old that was in the studio apartment. that was blissfully unaware and also so hopeful of what was going to happen. saying good-bye to my old normal. ma has to commit to living in a bigger, more complicated world, and that's what i have to do as well. >> you're going to love it. >> what? >> the world. >> thank you, robin. be sure to watch the 88th academy awards this sunday night at 8:30 right here on abc. next, he addressed the lack 2005. but how will chris rock confront the controversy this year? check this out, bro. what's that, broheim? i switched to geico and got more. more savings on car insurance? yeah bro-fessor, and more.

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i'm hillary clinton and i approve this message. her life's work has been about breaking barriers. and so would her presidency. which is why, for every american who's not being paid what they're worth... who's held back by student debt or a system tilted against them- and there are far too many of you- she understands that our country can't reach it's potential... unless we all do. together.

finally tonight, the buildup to the oscars has been exciting and highly controversial. who will dress the best, who will snatch the golden statues for best actor and actress, how will chris rock address the elephant in the room? here's abc's nick watt. >> reporter: ever since the lily white nominations were announced, chris rock has canceled all interviews. late last night tweeting, see you sunday #blackout. jada pinkett smith, will smith, spike lee are boycotting. not rock. he's hosting with millions eyeballs upon him. >> what you can expect from chris rock this oscar sunday is that he is going to go there. >> reporter: we know he will

not one black acting nominee. on twitter he already joked, the oscars are just white b.e.t. awards. >> our host for this evening, chris rock! >> reporter: this was last time he hosted in 2005. >> it's a great night tonight, we have like four black nominees tonight. so great, it's kind of like the def oscar jam tonight. >> reporter: with every hollywood mover and shaker in the room, 40 million plus of us watching at home -- >> if you get off on the wrong foot, it's a real hard hole to dig yourself out of. >> i think he might relish that challenge. >> i'm only here because ellen didn't want to do the show. know what i mean? i'm only here because ellen said no. >> reporter: other clues from his last time hosting, he will probably get political. >> bush did some things you could never get away with at your job. >> reporter: he will definitely get personal.

>> tobyey maguire is just a boy in tights. >> reporter: from the tv promos -- >> i might curse. >> reporter: he won't, we hope. we like to keep it clean at abc. but -- >> he is a safe choice. tuning in you want to see how far he's going to take things, what he's going to say. >> black movies don't have real names. you get names like "barbershop." that's not a name, that's a location. >> reporter: rock is publicly proud of hosting a very fast show last time. fast, furious, and funny. expect that. >> thank you! >> reporter: i'm nick watt for >> thank you! >> it was english actor and academy award winner peter yusanov who said, comedy is serious. we wish chris rock serious success sunday night. thank you for watching. tune into gma monday morning. as always we're online 24/7 on

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