ARI SHAPIRO, HOST:
The race for president is clearer today, much more so on the Democratic side. Hillary Clinton clearly won 4 of the 5 states that voted yesterday, and in the fifth state, Missouri, she holds a razor-thin lead. On the Republican side, Donald Trump won three states and advanced his delegate lead. NPR's Mara Liasson is back here once again to tell us what these results mean. Hey, Mara.
MARA LIASSON, BYLINE: Hi there.
SHAPIRO: Let's start with the Democrats. What did Hillary Clinton prove with her apparent sweep last?
LIASSON: She proved a lot of things. She proved she can win in an open primary where independents and people who aren't registered Democrats can vote. She proved she can win in a big battleground state, a big Rust Belt state, state with relatively smaller black vote, proportionally. In short, she could win in what we were coming to think of as Bernie country.
SHAPIRO: And just last week, Bernie Sanders won Michigan, and it seemed like he might do the same in the Rust Belt states that voted yesterday, but he didn't. Where did he go wrong?
LIASSON: He didn't, and it wasn't for lack of trying. He spent a lot of money. He spent $8 million on the air in the last five days. He outspent Hillary Clinton in 4 of 5 states, but she closed the gap with him on some issues.
She won voters who were concerned about trade deals, for instance. And it's possible that after the clashes between Trump supporters and protesters last weekend, Democrats started focusing more on the general election and thinking more about facing Donald Trump in the fall.
We also know from exit polls last night that Democratic voters, unlike Republicans, actually value experience. That's a Hillary Clinton strength. And so contrary to historical patterns, what we're seeing now is that Democrats are the unified party. They're the party that's falling in line, and the Republicans are falling apart.
SHAPIRO: Well, speaking of Republicans, Donald Trump last night won Florida, North Carolina and Illinois. What do those wins tell us about him?
LIASSON: Well, they tell us that he can win in a closed primary where only registered Republicans vote. That hadn't been a strength of his until last night. Granted, it was Florida, something of a home state for him. But he beat the favorite son there by 20 pints. So he still has the clearest path to the nomination of the remaining candidates.
But we also learned he's not unstoppable because if his populist pitch had broad appeal in a general election, you would think he'd be getting bigger and bigger margins as the primaries rolled on. That's what happened to previous Republican nominees like John McCain or Mitt Romney. The coalesce the party behind them even as they still had multiple opponents in the race. That's not happening with Trump. And unlike Hillary Clinton, there's now a growing possibility that he will show up in Cleveland without the 1,237 delegates he needs to win on the first ballot.
SHAPIRO: There was supposed to have been a Republican debate on Monday in Utah. It's been canceled. So how do Ted Cruz and John Kasich challenge Trump without debates?
LIASSON: Good question. Kasich performed an important function for the stop-Trump movement. He was a speed bump for Trump in Ohio. He denied him the unimpeded path to the nomination. But Kasich hasn't been able to win anywhere other than his home state.
Cruz, on the other hand, is lining up delegates for a second battle scenario in Cleveland. But today, Trump said if he comes to the convention with the most delegates and is denied the nomination, there will be riots.
SHAPIRO: Riots - well, as we are hearing elsewhere in the program, some conservatives are pushing to form a third party. There is no modern history of success there. What can they realistically gain by this effort?
LIASSON: Well, the strategy is to get conservatives and Republicans who won't vote for Trump or Clinton to come out and vote for Republicans for House and Senate. Otherwise, if they stay home, Republicans could lose down ballot. In last night's exit polls, 2 out of 5 Republican voters in every state but Florida told pollsters they would consider voting for a third party.
This really is a last resort if Trump can't be stopped at the convention. And we may be witnessing something that we've never seen in over a hundred years, which is the potential breakup of a major political party or at least the utter transformation of the Republican Party.
And Sally Bradshaw, who was the Florida Republican who ran Jeb Bush's campaign, said to Politico this week - she said, quote, "Donald Trump has done to the Republican Party what the killer comet did to the dinosaurs."
LIASSON: And she said there needs to be some rapid evolution between now and November if we hope to win.
SHAPIRO: Really interesting times in American politics - Mara Liasson, glad you're here to guide us through it.
LIASSON: Thank you. Transcript provided by NPR, Copyright NPR.