AUDIE CORNISH, HOST:
If Ted Cruz has any chance to get between Trump and the Republican nomination, he'll need an upset in Indiana. Today brought out some of the most explosive attacks between Cruz and Trump. Here to tell us more are NPR's Sam Sanders - he's following the Cruz campaign in Indianapolis; hey there, Sam...
SAM SANDERS, BYLINE: Hey. How are you?
CORNISH: ...And NPR's Don Gonyea in New York City where Donald Trump is now. Welcome back, Don.
DON GONYEA, BYLINE: Hi, Audie.
CORNISH: So I understand things got pretty ugly today with the National Enquirer and JFK conspiracy theories in the mix. Don, what's going on?
GONYEA: OK, so this is kind of the last burst of attacks that you sometimes see when a campaign is reaching its climax, right? Except this being 2016, it's in Technicolor. It's in all caps. It's in 3-D. What else can I add to that?
So right, here's the deal. There's this National Enquirer story that's actually been out for a couple of weeks. And without any proof, they say a photo of Lee Harvey Oswald shows Ted Cruz's father with Oswald just a few months before the assassination of President Kennedy. Again, there's no proof attached to this, but that was enough for Donald Trump to jump on it today in an interview with Fox News.
(SOUNDBITE OF ARCHIVED RECORDING)
DONALD TRUMP: What was he doing with Lee Harvey Oswald...
UNIDENTIFIED MAN: Right.
TRUMP: ...Shortly before the death, before the shooting. It's...
UNIDENTIFIED MAN: Crazy.
TRUMP: It's horrible.
GONYEA: OK, again, no proof that this is real. It was printed to the National Enquirer. But then Ted Cruz had a news conference. He defended his father and just unloaded on Trump.
(SOUNDBITE OF ARCHIVED RECORDING)
TED CRUZ: If you hooked him up to a lie detector test, he could say one thing in the morning, one thing at noon and one thing in the evening, all contradictory, and he'd pass the lie detector test each time. Whatever lie he's telling at that minute, he believes it. But the man is utterly amoral.
ROBERT SIEGEL, HOST:
Sam, you're following Ted Cruz in Indiana. Help us understand what's going on here that he felt he had to respond and respond so forcefully to this.
SANDERS: Yeah, you know, it seems like for Cruz, it's becoming a pattern where he gets distracted by Trump or even Trump supporters. There was this really awkward exchange on Monday where a Trump supporter was heckling Cruz, and Cruz engaged with this man for eight minutes as the guy called him a liar, told him to go back to Canada.
And today we see him in this back-and-forth with Trump. We're really seeing Trump, I think, and Trump supporters just get into Cruz's head and kind of get him off message. And I think that's in part because things aren't going well for Cruz. He's down in most polls, and there's talk of this being his last gasp. He's tried to do everything he can to change that narrative. He picked a running mate. He had a pact with John Kasich that seems to have fallen apart. But he's still trying.
SIEGEL: But is Ted Cruz likely to change any minds?
SANDERS: I mean, anything could happen, but this might not happen. The margins of Trump's wins in the last several states have only been growing. Cruz is down in the polls in this state, and now it is mathematically impossible for Cruz to win enough delegates to win the nomination on the first ballot at this summer's convention.
But Cruz's press conference today sounded like he was making a final push to the voters of Indiana to not take the country down what he has called a troubling path with Trump. And every Cruz supporter that I've talked to today and yesterday - they all say they want him to stay in it, that there is still a chance and that he could win this thing.
CORNISH: So Don, what would it mean if Trump wins big today as expected?
GONYEA: Well, going into today, Trump needed just 42 percent of all the remaining delegates. Again, that's before we allocate Indiana. Say he sweeps Indiana, which is possible. At that point, he'll need just over a third the rest of the way. So he doesn't clinch it today, but he becomes essentially unstoppable after today.
And there's this thing called inevitability. Nine in 10 Republican voters already think Donald Trump will be the nominee, so that brings people over to his camp as well and has people getting ready with the notion of him as their nominee.
CORNISH: That's NPR's Don Gonyea and Sam Sanders. Thanks to you both.
SANDERS: Thank you.
GONYEA: Thank you. Transcript provided by NPR, Copyright NPR.