When Democrats in Iowa kick off the presidential nominating contest Monday, they will begin to answer a momentous question poised to define the party for years: Whether the Democratic Party will continue to govern in the center-left mold of Barack Obama or revert to the economic-populist roots of Franklin Delano Roosevelt.

The 2020 primary has become a proxy war for the question, which divides the major candidates and channels a growing ideological and generational divide within the party.

It is evident in the closing messages of the front-runners. Joe Biden, Obama’s former vice president who frequently evokes him, proposes in an op-ed to "set America back on a path of decency, respect, and lasting progress." Bernie Sanders uses footage of FDR in a recent ad denouncing “half-measures” and saying that "America is best when we strive to do big things, even when it's hard."

On one side is an older and moderate cohort drawn to pitches by Biden — and to an extent, Pete Buttigieg — of finding common ground and unifying the country. Challenging them is a younger and re-energized left that wants a more aggressive nominee like Sanders or Elizabeth Warren who will seek to bust corporate power, expand the safety net and finish the project FDR began.

“Senator Sanders is the fulfillment of the FDR legacy,” said Rep. Ro Khanna, D-Calif., one of his prominent endorsers. “I believe we are at a moment in history where, post-Trump, we could see the dawn of a new progressive era. If you believe that moment hasn’t come and we just need to defeat Trump and return to normalcy, then Vice President Biden is offering that choice.”

Moderates have dominated the party ever since Bill Clinton won in 1992 by recapturing the political center after Democrats suffered three landslide defeats in the 1980s. But in recent years the left has found its way out of the wilderness and moved ideas such as Medicare for All, free public college and a $15 minimum wage from the left fringes of the party into the mainstream.

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“It’s going to have major consequences if the FDR side of the party wins. It shifts the paradigm completely. We will essentially be shifting to a more socialist form of government,” said Adrienne Elrod, a Democratic strategist and former senior adviser to Hillary Clinton’s 2016 campaign. “The Obama wing of the party has a totally different vision of how to achieve shared goals than the FDR wing of the party.”

Elrod said a victory by Sanders would likely push economically moderate voters out of the party while also bringing in enough voters who have felt alienated by traditional Democratic Party politics to “pull together a winning coalition if he’s the nominee.”

“There are a lot of Democrats who still feel like this country is not fighting for them and our government is not fighting for them. They think the Obama administration didn’t do enough and they look at Bernie and say, let’s have full fledged Medicare for All,” she said. “Let’s have free college because myself and my kids are saddled with tens of thousands of dollars in debt.”

Warren is also competing for the mantle of Roosevelt, the father of the U.S. safety net who signed Social Security into law and built a movement to transform the U.S. “She is the FDR I'm looking for — to make big structural change that virtually everybody wants, except in the insurance industry and big pharma and Wall Street,” Rep. Andy Levin, D-Mich., a Warren surrogate, told reporters.

But the party's national front-runner has a different view.

Biden’s advisers see a Democratic electorate that is older, more moderate and less interested in radical change than the loudest voices on social media. They point to Obama’s towering favorable rating among Democrats as evidence that voters want a pragmatist. And they say the party’s voters view Trump as a uniquely threatening president and are motivated more by a desire to defeat him than by a particular ideological vision.

“There’s only one stake: beating Trump,” said Joe Trippi, an unaligned Democratic strategist and presidential campaign veteran.

Trippi said the clash of visions is less important to the party’s voters than the question of who can defeat the president, and current surveys show pluralities of Democrats believe Biden is best-positioned to win the general election. “Democrats would happily take either one of those paths if they thought that was the path that could beat Trump,” he said.

The conservative pro-Trump group Club For Growth Action is seeking to exploit the Democratic split with a new ad: “More radical than Obama on health care, Bernie's plan gives government health insurance to everyone. His socialist Green New Deal? Even bigger than the New Deal,” a narrator says as the spot shows images of Obama, Sanders and Roosevelt.

Whether Democrats can usher in an era of radical change depends on the magnitude of a far-from-certain victory — including whether the party recaptures control of both houses of Congress.

Republicans are highly unlikely to cooperate and plenty of Democrats in both chambers prefer incrementalism. An FDR-style coalition that wins Democrats more than 40 states is virtually unimaginable today in a country gripped by negative partisanship and divided along ethnic and educational lines, among others.

Unlike FDR-era contemporaries, today's Democrats are unanimously in favor of socially progressive policies on immigration, abortion rights and racial justice. The big question facing Democratic voters this year is which of the two economic paths they want to pursue.

“One coalition is talking about essentially moving things modestly in a more liberal direction and the other one is talking about massive systemic reform,” said Seth Masket, a political science professor and director of the University of Denver’s Center on American Politics. “There’s clearly been some sort of latent movement toward more substantial change. We haven’t seen factionalism within the Democratic coalition like this since the ‘60s and ‘70s.”