LOURDES GARCIA-NAVARRO, HOST:

One of the most important forces in American politics today is populism. In both the Democratic and Republican races, politicians are tapping into widespread frustrations against the elites and the establishment. NPR's national political correspondent, Mara Liasson, has been watching this trend, and she's here to tell us more. Hey.

MARA LIASSON, BYLINE: Hi, good morning, Lourdes.

GARCIA-NAVARRO: So what were you interested in finding out, exactly?

LIASSON: I was interested in finding out what this populism means. We know that Bernie Sanders and Donald Trump are riding this populist wave. But I wanted to see what effects populism might have on both parties in the longer term.

GARCIA-NAVARRO: So where did you go to look at that?

LIASSON: I started by calling Mudcat Saunders. He's a hillbilly, and he's proud of it. He lives up a hollow in southwestern Virginia. And as you'll hear soon, he had to drive up to the top of the hill near his house to get any cell reception. But Saunders is also a Democratic political strategist. And this year, he sees a lot of overlap between the populism of Donald Trump and Bernie Sanders.

MUDCAT SAUNDERS: I call it the great new age of economic populism, where I live. I don't think it's just a lot of Trump people. And they're obviously there, but at the same token, we've got tons of Bernie people here. And it's all the same thing. It's about populism. It's about economic fairness, and we feel like we've been left behind.

LIASSON: Kathy Cramer is a political science professor at the University of Wisconsin. And for the last 11 years, she's been tracking the increasingly populist sentiments of Wisconsin voters by listening to groups of people who meet on their own most every morning.

KATHY CRAMER: They're kind of what we might call regulars in gas stations and diners and McDonald's and maybe places of worship.

LIASSON: Cramer says these groups foreshadowed the angry voters of 2016. They felt ignored or dismissed by politicians, the media, the government, big business. And over the past nine years, what Cramer saw was that this resentment grew more intense, setting the stage for the explosion of populist politics this year.

CRAMER: What I saw was people feeling a whole lot of economic stress, wanting some explanation for why they were having such a hard time making ends meet and then placing the blame on other people in the population and the government.

LIASSON: We know what the big forces of change are - demographics, globalization, deindustrialization. But those are pretty abstract and can be hard to understand. On the other hand, populism has always told a simpler story with a defined villain. In the past, it might have been the gold standard or minorities. Now it's free trade, immigrants, billionaires or the campaign finance system.

CRAMER: The things that are our biggest stresses these days are these very abstract, social change phenomena, right? And making an argument about that doesn't get you very far. It's not very mobilizing. But yes, if you can give people a crystal-clear target of blame, it's much easier to rally people behind you.

LIASSON: On the Republican side, the new populism isn't actually new. Michael Lind is with the New America Foundation. He told me that Donald Trump didn't just come from nowhere. He's an example of how Republican politicians are catching up with how their base feels about immigration and entitlement reform. Lind reminded me that back in 2005, George W. Bush's immigration reform plan and his plan to partially privatize Social Security both failed, partly because the Republican base was against them.

MICHAEL LIND: So in a sense, Trump is merely articulating views on middle-class entitlements and on immigration, which the Republican base already has shared and acted on for a decade or more.

LIASSON: In the past, populist movements have forced a realignment or a reshuffling of voters. But Lind says that's already happened. There's not many socially conservative, economically populist white Democrats left that could switch to the Republicans. And there's not that many socially liberal, upscale white Republicans left who could switch to the Democrats.

LIND: I think the party coalitions are pretty well defined. And in the energy, really, the civil wars within the parties is about defining the party platforms more than the party coalitions.

LIASSON: For the Republicans, that civil war might lead to a debate about a new policy agenda. And it could produce a new agenda that's less friendly to big business and the wealthy and more attuned to the concerns of the white working class. I also talked to Henry Olsen about this. He's the author of "The Four Faces Of The Republican Party." And he says that is the lesson of this year's Republican primaries.

HENRY OLSEN: Any ambitious politician has seen that there are millions of voters who can be mobilized using populist rhetoric who had not voted in any Republican presidential primary for the last 20 years. And you probably won't see an identical Trump-like figure in future years. But anti-trade, more nativist, more anti-free markets are there for the taking in the Republican Party. And that will influence campaigns and candidates for years to come.

LIASSON: And Olsen said that could lead the GOP to rethink its across-the-board commitment to limited government. Now, on the Democratic side, Bill Galston, who worked for Bill Clinton in the White House, sees Bernie Sanders leading a similar populist revolt but without the same seismic consequences for his party.

BILL GALSTON: There's a lot of economic discontent among young adults, the working-class and the middle-class. So there's something real there for Democrats. And it's not going away.

LIASSON: One consequence for both parties, Galston says, is that free trade agreements will have to be reframed as national security issues in order to have any chance at all to pass. And whoever is making foreign policy next year will have to deal with a new kind of nationalism. Galston calls it Americans first.

GALSTON: What that means is that whether people who are looking at the world through populist spectacles - their first question is now, what's in it for us? And if there isn't a clear answer to that question, then the default conclusion is that what's going on beyond our borders is more of a burden than a benefit.

GARCIA-NAVARRO: So Mara Liasson, it sounds like populism is affecting both parties, but it's much more disruptive for the Republicans.

LIASSON: That's right. Donald Trump's positions are challenging the Republican Party's basic DNA, their core ideology about foreign policy and trade and limited government. On the Democratic side, Sanders doesn't represent a break with Democratic orthodoxy. He represents a wing of the party that's always been there. It's just gotten to be a much bigger part of the Democratic coalition this year.

GARCIA-NAVARRO: Some would argue that this unsettling moment in American politics was much needed. Where do you think this is headed?

LIASSON: Well, in the past, there have been a populist movements in American politics. And sometimes they lead to great bursts of progressive reform. And sometimes they lead to nativism and isolationism. We just don't know where this one is going to end up.

GARCIA-NAVARRO: NPR's national political correspondent, Mara Liasson Thank you so much.

LIASSON: Thank You.