With less than three weeks before the first-in-the-nation caucuses in Iowa, the breakdown of a long-standing nonaggression pact between the two leading liberals in the race cast doubt on whether Sanders or Warren could unite the Democratic Party’s liberal wing.

Polls in Iowa and New Hampshire have found all of the top candidates — Sanders, Warren, former Mayor Pete Buttigieg of South Bend, Indiana, and former Vice President Joe Biden — bunched up in the earliest Democratic contests, though Biden has held a steady national lead, helped to a great degree by divisions on the left. ​ ​

The rupture, which has already angered supporters of Warren and Sanders, could heighten Democratic anxieties and inject negativity into the race in Iowa, where Democrats have a history of rewarding positive behavior from presidential candidates.

“I think you called me a liar on national TV,” Warren told Sanders after the presidential debate in Des Moines on Tuesday night, referring to their earlier dispute onstage over whether he told her in a private 2018 meeting that a woman could not be president. The New York Times described details of their exchange on Wednesday afternoon, and CNN broadcast an audio recording that night.

According to the audio, Sanders responded, “What?”

“I think you called me a liar on national TV,” she said again.

“You know, let’s not do it right now,” he said. “If you want to have that discussion, we’ll have that discussion.”

Warren replied, “Anytime.”

“You called me a liar,” Sanders said. “You told me — all right, let’s not do it now.”

Tom Steyer, the billionaire businessman, approached Sanders in the middle of the exchange.

“I don’t want to get in the middle,” Steyer said. “I just want to say, ‘Hi, Bernie.’”

Both the Warren and Sanders campaigns declined to comment Wednesday.

The exchange onstage between the two progressives, surrounded by onlookers but wrapped up in their intensely personal rivalry, marked their most direct confrontation in the entire 2020 election. And in some respects, it represented a kind of inevitable concession to reality: If Warren and Sanders share an ideological cause, up to a point, they cannot ultimately share a presidential nomination. For Warren, taking on Sanders face-to-face risked further angering the far left, sections of which have already turned on her for her rivalry with Sanders. And while Warren was praised for addressing the subject of gender head-on during the debate, even some of her supporters acknowledge that tackling sexism so prominently could risk leaving primary voters uneasy about the implications of nominating a woman.

Progressives fear the public division will benefit the moderates in the race — and, more broadly, threaten the movement they have tried to build. Leading progressive groups spent hours Wednesday trying to craft joint statements of unity while their leading political figures were in a public fight.

“I am hoping that volunteers and grassroots groups can help bridge the gap that has opened between Warren and Sanders around their 2018 conversation,” said Larry Cohen, a longtime friend and adviser to Sanders who serves as chairman of Our Revolution, the organization that spun out of the 2016 Sanders campaign. “We remain focused on racial and gender justice, health care, climate crisis, good jobs, student debt and free college, the spiraling military budget and more. I don’t see a path forward on those issues in the Senate or at the Democratic National Convention in Milwaukee without cooperation when the time comes.”

Many progressive leaders pointed to the 2004 primary as a cautionary tale, when feuding between the more liberal candidacies of Rep. Richard Gephardt of Missouri and former Gov. Howard Dean of Vermont helped the more moderate Sen. John Kerry of Massachusetts win the Iowa caucus after a summer slump.

“It’s absolutely critical that progressives focus their fire on the corporate wing of the party to not allow a repeat of the 2004 election,” said Neil Sroka, communications director for Democracy for America, a liberal group founded by Dean after his unsuccessful primary run.

For Sanders, there is little upside to a drawn-out clash with Warren, particularly over matters of gender and sexism. While Sanders’ hard-core base has rallied to his side, much of the Democratic electorate still harbors feelings of resentment toward Sanders for his conduct toward Hillary Clinton during the 2016 presidential primaries.

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And in a conflict heavily focused on which candidate is telling the truth, Warren faces a real risk: Several studies have shown that voters punish women more harshly than men for real or perceived dishonesty.

Depictions of female candidates as calculating or conniving are political mainstays. As long ago as 1984, opponents launched “authenticity” attacks against Geraldine Ferraro, the first woman to appear on a major party’s presidential ticket. This pattern endures regardless of who is telling the truth, these studies conclude, and regardless of either candidate’s intentions. If voters conclude that Warren is lying, it is likely to hurt her more than it would hurt Sanders if voters concluded that he was lying.

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It is unclear whether either candidate might be inclined to perpetuate the feud in public. It is telling that Warren’s most pointed comment to Sanders came after the formal debate concluded, and that Sanders responded not by escalating the fight but by deferring it to another time.

By the time CNN aired the footage, the two candidates had not spoken about the exchange, people familiar with their whereabouts said, though they are expected to be in close contact when the Senate convenes Friday.

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CNN executives initially said they did not believe the exchange had been captured by the network’s microphones. The network said its journalists located a recording late on Wednesday after reviewing audio from the microphones that Sanders and Warren had been wearing onstage.

Over the weekend, Warren said she was “disappointed” in Sanders after Politico reported that his campaign had distributed a script to volunteers suggesting she appealed mainly to highly educated voters. On Monday, CNN reported that Sanders had told Warren in a private meeting in 2018 that he thought a woman could not win the presidency; Sanders vehemently denied it.

“I thought a woman could win; he disagreed,” Warren said in a statement on Monday.

On Tuesday, the issue burst forth onto the debate stage in a remarkable moment before a national audience that captured the recent friction between the two senators.

“I didn’t say it,” Sanders insisted, about her characterization of his 2018 remarks. Warren disputed that, then called him her friend before pivoting to make the case that of the six candidates onstage, only the women had won all of their elections.

After the debate, Steyer repeatedly insisted he did not hear the back-and-forth between the two liberals.

“I was just saying good night to the two of them,” he told reporters during a brief exchange in the debate spin room at Drake University. “I didn’t hear anything.”

This article originally appeared in The New York Times .