RACHEL MARTIN, HOST:

Democrats in New York vote as well on Tuesday. New York Times columnist Frank Bruni has been watching Bernie Sanders and Hillary Clinton make their respective cases. And he joins us now live. Good morning, Frank.

FRANK BRUNI: Good morning.

MARTIN: You've been writing about these two candidates for months. At this point in the race, has all the campaigning made them better candidates? Or has it done more to expose their weaknesses? Let's start with Bernie Sanders.

BRUNI: Well, you know, it's done a little bit of both. In Bernie's case - in mister - Senator Sanders's case, it's interesting because it's difficult to go through a campaign this long and not end up seeming more like a conventional politician than you did at the start. You know, of course he came into this running a different kind of campaign, coming from a very different direction than other Democratic candidates for the nomination have come. And he was, in many ways, trying to transcend politics as usual. A long campaign is politics as usual and you end up seeming less pure, less high-minded, more like everybody else. And in that sense, I think his campaign - his candidacy has sullied him a little bit.

MARTIN: And for Hillary Clinton.

BRUNI: Well, you know, we knew Hillary Clinton so well going in. I don't think we've learned a lot new about her. The main thing we've seen with her is that there are very, very finite limits to her appeal. And I think there was a sense of that beforehand, but it's been validated by this campaign. Her unfavorable ratings remain pretty high. She hasn't been able to turn that around. And if the GOP wasn't suffering a sort of implosion of its own, I think there would be great worry about her prospects in a general election. But she may get the incredible break of a very, very weak controversial Republican nominee against her.

MARTIN: That's assuming a lot. I mean, who knows how the Republican primary is going to end up. And if she is the nominee, how does she bridge that enthusiasm gap? I mean, we've seen this huge enthusiasm, all these crowds for Sanders. She's got to figure out how to bring them under her tent. And is there a kind of a political risk in this era in framing yourself as the safe choice?

BRUNI: (Laughter) There's always a risk in that because you need turnout. You need people to be passionate about you. And saying I'm safe and sensible is not a very romantic pitch.

I think what happens if she becomes the nominee - and you're right, I made a lot of assumptions a moment ago - if she becomes the nominee, I think what happens, sadly, is she tries as much to convince people of how horrible the other choice would be as how good she is. And we end up, I think, with quite a negative campaign, which it won't be the first time. But the problem with that is when we have these negative campaigns and then someone ends up in office, it becomes very difficult to govern because you created such a - such an atmosphere of enmity that when you then need people to come together to make decisions and progress, it's difficult.

MARTIN: You wrote this past week in your column that the split within the Democratic Party has been obscured by all the drama on the GOP side, but that there is real trouble within the Democratic Party. What are the fault lines as you see them?

BRUNI: There are a number of fault lines. I mean, one is in foreign policy. You saw this fault line very, very clearly in the debate in Brooklyn. Hillary Clinton talked a lot about the value of foreign interventions. And Bernie Sanders talked a lot about the folly and shortsightedness of so many of them. That's a very big fault line in the Democratic Party. Then there's a big overarching fault line, which is whether we need to tinker with and improve the system as it is or sort of throw it out and begin anew. Bernie Sanders is sort of saying the latter. And Hillary Clinton's saying no, I've worked within the system. Only certain kinds of changes are possible. I know where we can tinker. So it's sort of revolution versus tinkering - is a big fault line.

MARTIN: And you think that's a problem that extends beyond these two candidates? It's something that's a problem at large for the party?

BRUNI: Absolutely. I don't think people are responding to Bernie Sanders - there's many, many supporters - just because he's such a great candidate. I think they're responding to the ideas that he's promoting, to what he represents. They're some of the same people who have been so excited about Elizabeth Warren. So it's bigger than him. And I think it will survive this contest. I think it's something we'll be dealing with over the next decade.

MARTIN: New York Times columnist Frank Bruni. His latest book is titled "Where You Go Is Not Who You'll Be." Thanks so much, Frank.

BRUNI: Thank you very much. Transcript provided by NPR, Copyright NPR.