DES MOINES, Iowa — The sharp left turn in the Democratic Party and the rise of progressive presidential candidates are unnerving moderate Democrats who increasingly fear that the party could fritter away its chances of beating President Donald Trump in 2020 by careening over a liberal cliff.

Two months into the presidential campaign, the leading Democratic contenders have largely broken with consensus-driven politics and embraced leftist ideas on health care, taxes, the environment and Middle East policy that would fundamentally alter the economy and elements of foreign policy and ultimately remake American life.

Led by Sen. Bernie Sanders of Vermont, a democratic socialist who is the top candidate in the race at this early stage, many vocal leaders in the party are choosing to draw lessons from liberal victories in 2018 rather than the party’s breakthroughs in moderate suburban battlegrounds that delivered Democratic control of the House.

These progressive Democrats risk playing into Trump’s hands — he has repeatedly branded them “socialists” — yet they argue that their ambitious agenda can inspire a voter revolt in 2020 that elects a left-wing president.

“Those ideas that we talked about here in Iowa four years ago that seemed so radical at the time, remember that?” Sanders, returning to Iowa for the first time as a 2020 candidate, crowed Thursday. “Shock of all shocks, those very same ideas are now supported not only by Democratic candidates for president but by Democratic candidates all across the board, from school board on up.”

The sprint toward populism amounts to a rejection of the incremental and often-defensive brand of politics that has characterized the party’s approach to highly charged issues for 40 years. Yet when nearly half of voters indicate in polls that they will not support the president’s re-election, many moderates say the cautious strategy in 2018 that helped the party pick up 21 House seats that Trump carried two years earlier should be the playbook for next year.

“What we saw in the midterms is a lot of people from the center and moderate part of the party really win and take back the House,” said Sen. Maggie Hassan of New Hampshire, alluding to the careful and poll-tested campaigns many Democrats in Republican-leaning districts ran last year. “We need to make sure we’re being as pragmatic as we can.”

This moderate wing of the party lacks an obvious standard-bearer. Former Mayor Michael Bloomberg of New York, who would have run a centrist campaign, begged off this past week; Sen. Sherrod Brown of Ohio, a Midwestern progressive who favors a within-the-system style of pragmatic politics, also decided not to run. Sen. Amy Klobuchar of Minnesota, who is running, has presented herself as a centrist but has not yet gained traction.

Should former Vice President Joe Biden enter the race, as his top advisers vow he soon will, he would have the best immediate shot at the moderate mantle. (And if he does not run, Democrats like former Gov. Terry McAuliffe of Virginia or Gov. Andrew Cuomo of New York might try to seek that role.)

Biden’s candidacy would immediately thrust a fundamental dispute to the center of the Democratic race: Do Americans simply pine for a pre-Trump equilibrium, less chaos and more consensus, or do the yawning disparities of these times call out for a more transformational administration?

Sanders and other Democratic candidates, like Sen. Elizabeth Warren of Massachusetts, are plainly wagering that voters want more than a return to normalcy.

“In 2016 Iowa helped begin the political revolution,” Sanders recalled Saturday at a rally in Des Moines, referring to his near-victory in the state’s caucuses that year. “Now as we move to 2020 our job is to complete that revolution.”

The liberal candidates have dominated the policy debate in the race so far. Warren proposed Friday that the government break up big tech giants like Amazon and Facebook, the latest, and perhaps boldest, proposal to come from her campaign. And Sanders’ platform — “Medicare for all,” free college tuition and an aggressive plan to combat climate change — has grown in popularity, according to polls.

Speaking at the University of Iowa as part of his campaign swing, Sanders also took aim at “establishment Democrats” and won his loudest and most sustained applause by pledging to push through his universal health care bill.

Sanders and Warren, along with a new generation of high-profile progressives like Rep. Alexandria Ocasio-Cortez of New York, have emerged this winter as the clearest and most vocal arbiters of Democratic aspirations, if not the immediate congressional agenda.

They are, at least, hastening the tectonic shifts taking place in the party. It was no accident that House Democrats modified a resolution targeting Rep. Ilhan Omar of Minnesota — for her controversial claim that pro-Israel advocates carry an “allegiance” to a foreign country — after Ocasio-Cortez, other lawmakers of color and the party’s leading presidential hopefuls rebelled against singling out Omar. The episode marked a striking departure from the down-the-line support for Israel that has characterized the upper ranks of most Democratic primaries.

Relying on wealthy donors has also been standard fare, and unremarkably so, in past White House races. But Sanders elevated the issue of campaign finance in his 2016 race, and his jeremiads against the billionaire class have all but made super PACs verboten in this race; he and Warren are refusing to hold high-dollar fundraisers.

Rep. Ayanna Pressley of Massachusetts, who won her seat after defeating an incumbent Democrat last year, conceded that the first months of 2019 had inflicted “growing pains” on Democrats, but she argued it was merely a necessary side effect in the party’s evolution.

“After we build that muscle, we’re going to flex it,” Pressley said.

Yet Biden, in speeches at home and abroad, has used much of the first part of this year pledging to restore the dignity he believes that the country has lost in the Trump years, promising a restoration rather than a revolution. And, as his supporters put it less subtly, his campaign would represent something else.

“Overwhelmingly, the primary electorate of the Democratic Party wants to win,” Sen. Chris Coons of Delaware said. He argued that Biden could “repair a lot of the ways in which our position in the world has been harmed” while offering a “hopeful, optimistic, positive” vision at home that would heal the divisions he said Trump has exacerbated.

To such moderate Democrats, the most instructive recent election is not that of Trump in 2016 but rather the 2018 midterms, when many of the Democrats who won in battleground House districts and governor’s races were decidedly less confrontational than Sanders.

“The overwhelming majority of seats we picked up were by center-left candidates representing more centrist-type districts,” said Rep. Brendan Boyle of Pennsylvania, adding, “There’s still lots of folks on our side who are OK with compromise.”

Other Democrats are even blunter, fretting that the party risks alienating the broad middle of the electorate at a moment Trump is making no attempt to appeal to such voters.

“You live for the day in politics when the other guy is conceding the majority of the country,” said Larry Grisolano, a longtime Democratic strategist.

Yet for many Democrats — especially younger voters who have largely known only Trump and another once-unlikely president for eight years before that — it is a hopelessly outdated notion that the party must be prudent about whom it nominates and tread only within centrist confines on animating issues like climate change, racial justice and universal health care. These progressives have no more experience with a right-of-center, Reagan-era framework than their parents did with the New Deal.

“We have had enough of the centrist, corporatist Democratic — the type of Democrat that my mom would have voted for back in the ‘90s,” said Jake Peters, a 23-year-old Iowan and Sanders volunteer who drove two hours to see him speak in Council Bluffs this past week. “We just don’t have patience for the platitudes.”

And Trump has emboldened these young activists, heightening the urgency they feel about enacting a progressive agenda and convincing them that Sanders’ blunt-force message about injustice is what’s needed to defeat the president. Chris Kivlahan, 22, who came to the Iowa City rally, described a Sanders presidency this way: “I think if it’s going to happen, now is the time and Trump is the candidate to be running against.”

Democrats in Washington are seeing the tensions within the party firsthand as they try to balance an agenda that their newly elected moderates can support while also mollifying more liberal newcomers who are eager to impeach Trump and pursue far-reaching goals, such as the Green New Deal.

“A lot of young people have come into a world where there was more diversity, more opportunities and where they had use of social media,” said Rep. Elijah Cummings of Maryland about the expectations of next-generation activists and lawmakers, some of whom serve on the oversight committee he chairs. “A guy like me, I had to fight to even get in the door.”

To tell some of these younger Democrats that a uncompromising progressive platform may be unattainable, let alone who can and cannot be elected president, is difficult given Trump’s victory and the chasm they see between the scale of the problems they will confront and the policies in place today.

And unlike many in the party’s pragmatic wing, these Democrats believe the recipe for success in the general election is not to nominate another seemingly safe candidate like Hillary Clinton, who was unable to galvanize the base and lost crucial votes to a Green Party nominee, but to put forward somebody who will energize reluctant voters.

“Obviously we’ve shown that we’re at a place where we’re OK with nontraditional candidates,” said Riley Wilson, a 29-year-old Nebraskan who crossed the Missouri River to see Sanders. He added: “I think so many people just aren’t involved at all in politics, and I think he would be able to bring some of those people into the fold because they’ll feel like they have options that they haven’t had before, politically speaking.”

And about the Republican strategy, led by Trump himself, to pin the “socialism” label on the Democrats in 2020?

Sen. Brian Schatz of Hawaii said it was mostly just his party’s elite “donor class” that had anything to fear from a sweeping, progressive agenda.

Well, them and the arbiters of conventional political wisdom, he added.

“What we’ve learned from last two presidential elections is that nobody knows anything,” Schatz said of the election of former President Barack Obama and Trump. “The people who write op-eds and stroke their chins and tell us how to win are the people who have been getting it wrong for almost two decades now.”

This article originally appeared in The New York Times.