MELISSA BLOCK, HOST:

Primaries in five big states brought more delegates to front-runners Donald Trump and Hillary Clinton this week, but they didn't bring much more clarity to the outlook. Trump's field of opponents is now down to two, and his path to a first ballot win at the convention remains uncertain. Clinton is far ahead in delegates, but the Sanders campaign continues to contest the thousands of delegates still to be awarded.

Joining us to talk about what's happened and what's ahead is NPR senior editor and correspondent Ron Elving. Ron, good morning.

RON ELVING, BYLINE: Good to be with you, Melissa.

BLOCK: And what would the outlook be? If you want to stop Donald Trump from getting the Republican nomination this summer, what has to happen?

ELVING: What has to happen is either that the other candidates in the race have to keep him from reaching the 1,237 magic number that gives him a first ballot nomination or the party has to figure out some way to keep him just below that number and then turn on a second or third ballot to some other - at this point - unnamed candidate.

BLOCK: At a contested convention.

ELVING: Yes.

BLOCK: Let's talk about the Democratic side for a second. Hillary Clinton lost in Michigan to Bernie Sanders, went on to win all five primaries this week. Was that a surprise?

ELVING: It was a surprise in a couple of those states. Missouri looked like it was going to be close, and it was close, but she eventually pulled it out at the buzzer if you will. Illinois was also close, even though that was a state where she grew up.

But Ohio - she won with 56 percent. That was enormously impressive after the Michigan loss and she was always expected to win big in Florida and North Carolina. She won especially big in Florida.

BLOCK: And looking ahead to the upcoming primary states, what sort of pattern do you see that might emerge?

ELVING: Arizona on Tuesday looks like a crucial test right now of the momentum in the Clinton campaign. It should be a good state for Bernie Sanders because he's been working it really hard. He's had some big, boisterous rallies there. He's got a lot of support from Latino legislators, but the only polling that we've seen still has Hillary Clinton ahead. So we'll see where the momentum lies when we get to Tuesday and Arizona. It should also be a good state for Donald Trump.

BLOCK: We have seen Bernie Sanders do really, really well with young voters. How is Hillary Clinton trying to deal with that and to bring them over to her side?

ELVING: Well, Sanders has totally owned the under 30 vote - 85 percent.

BLOCK: Yeah.

ELVING: And the millennials, as we call them, have been very excited about the Sanders candidacy and about some of the issues he's raised about income inequality and so on, so it's an attachment to him. It's also perhaps a lack of enthusiasm for her. So we have seen her adopting some of his themes, speaking in some of his language, talking about - well, let's put it this way. It's gotten all the way to the point where "Saturday Night Live" did a whole mock ad of her turning into Bernie Sanders.

(SOUNDBITE OF TV SHOW, "SATURDAY NIGHT LIVE")

KATE MCKINNON: (As Hillary Clinton) I know you millennials. You're fired up. You're angry and I'm angry, too, because the top 10 percent of the top 1 percent controls 90 percent of the wealth in this country.

(LAUGHTER)

MCKINNON: (As Hillary Clinton) And I've always said that, ever since I was a young boy growing up in Brooklyn (laughter) Brooklyn.

(LAUGHTER)

BLOCK: And, Ron, visually, what's going on here?

ELVING: She is gradually using her hands more and more, waving them over the top of her head. And then, of course, as she moves through the edge, she is wearing a man's suit and then finally she has just a little crown of white hair on the top of her head and a pair of glasses on.

BLOCK: (Laughter) Ron, we mentioned earlier the talk about contested conventions this summer. What are the odds, do you think, that that might happen on either side?

ELVING: On the Democratic side, it would really depend on Bernie Sanders getting ahead among the pledged delegates and then contesting the superdelegates. These are people who get to go because of their elected office or because they're party officials. And that does not seem to be a strong prospect at this point.

But on the Republican side, maybe 50-50 because if Donald Trump does not get to the magic number, and maybe that would be because the other candidates were doing better than they have done, maybe it would be because he just sort of ran out of time. Either way, there are going to be strong forces within the party, anti-Trump forces, that are going to do anything that they can to deny him the nomination. They don't have a horse to ride yet. They don't really have a strategy. All they know is they think Donald Trump would be a disaster for the party in November.

BLOCK: NPR's Ron Elving. Ron, thanks so much.

ELVING: Thank you, Melissa. Transcript provided by NPR, Copyright NPR.

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