MELISSA BLOCK, HOST:
This is WEEKEND EDITION from NPR News. I'm Melissa Block. Rachel Martin is away. Here's the shape of the presidential contest as we look forward. Donald Trump is now the de facto Republican nominee. And on the Democratic side, Hillary Clinton is still the clear front-runner with a wide lead in delegates over Bernie Sanders.
But the primary race isn't over, and Trump and Clinton have a long to-do list as they head into an apparent general election matchup. NPR national political correspondent Mara Liasson joins us now. And Mara, let's start with Donald Trump, who finally, this week, consolidated his hold on the Republican nomination, but at the same time has exposed very deep divisions in his party.
MARA LIASSON, BYLINE: That's right. He's been trying to unify the party, but that hasn't happened yet. Instead, the civil war inside the Republican Party has burst out into the open. The two former living Republican presidents, George H.W. Bush and George Bush, are not endorsing Trump. Lots of senators and Congress members say they can't endorse.
And in the biggest split of all the speaker of the House, Paul Ryan, who is the highest-ranking Republican in the government and the chairman of the Republican convention this summer, has said he can't endorse Trump yet, saying Trump needs to make big changes in tone and substance. Donald Trump said he was blindsided by Ryan's comments. He fired back saying well, I'm not ready to support Ryan's agenda either. And this Thursday, the two men will meet at the capital with other Republican officials. And we'll see if they can get on the same page.
BLOCK: Yeah, it did seem that Paul Ryan did leave something of an open door there to a future endorsement. What's behind his thinking?
LIASSON: Some of it is strategic. He wants to protect his members, who are very worried about a negative down ballot toxic Trump effect. He said he's going to come up with an alternative policy agenda for Republicans to run on, but he doesn't have one yet. He - it also could be about 2020. Paul Ryan might have ambitions to run for president himself in four years.
Also, Ryan's feelings have been very strong about Trump. He's already spoken out about Trump's comments about banning Muslims, his reluctance to disavow a KKK endorsement. He's talked about the danger of identity politics, meaning white identity politics. He disagrees with Trump on trade. So Ryan's comments have the added benefit of being a true reflection of his feelings.
BLOCK: Let's talk about some of the down ballot races this cycle, Mara. This past week, we heard Sen. Kelly Ayotte of New Hampshire, who's up for re-elections, say that she plans to support Donald Trump, but not endorse him. I'm not quite sure what the distinction is that she's drawing.
LIASSON: (Laughter) I don't think anybody knows. The Republican Senate candidates have been tying themselves up into pretzels around Donald Trump. They've all been giving some version of I support the Republican nominee, but I'm not endorsing Donald Trump. That doesn't really make sense. And already, Democrats are running ads and issuing press releases trying to tie all the vulnerable Republican Senate incumbents to Trump.
And the incumbents who are running want to separate themselves from the top of the ticket. That's very hard to do. Just ask all those red state Democrats who lost their jobs in 2010 and 2014 - and Obama wasn't even on the top of the ticket in those races.
BLOCK: Let's talk about the Democratic race. Hillary Clinton, as we say, still the clear front-runner. But she lost to Bernie Sanders this past week in Indiana, and Sanders is heading into really favorable territory in upcoming primaries.
LIASSON: Yes, the upcoming primaries are good for Bernie Sanders, but the math still doesn't work for him. Hillary Clinton could lose all the remaining primaries by 20 points and still win. And even if you accept Sanders' argument that superdelegates should vote the way their states did and he got the same percentage of superdelegates in each state as he got the percentage of the vote, he'd still lose. So it's really mathematically impossible for Bernie Sanders to get the nomination at this point.
BLOCK: NPR's Mara Liasson. Mara, thanks.
LIASSON: Thank you. Transcript provided by NPR, Copyright NPR.