DES MOINES — The sudden clash between Senators Elizabeth Warren and Bernie Sanders over gender and honesty threatened to throw the Democratic presidential race into turmoil, after the publication on Wednesday evening of a recording that showed Ms. Warren and Mr. Sanders trading accusations that each had called the other a “liar” and attacked the other’s character.
With less than three weeks before the first-in-the-nation caucuses in Iowa, the apparent breakdown of a longstanding nonaggression pact between the two leading liberals in the race had the potential to upend what has been a tight contest, thrusting an explosive debate about matters of identity and personal integrity to the forefront of the campaign and perhaps imperiling the ability of Mr. Sanders or Ms. Warren to wrap up the nomination quickly by uniting the Democratic Party’s liberal wing.
Polls in Iowa and New Hampshire have found all of the top candidates — Mr. Sanders, Ms. Warren, former Mayor Pete Buttigieg of South Bend, Ind., and former Vice President Joseph R. Biden Jr. — bunched up in the earliest Democratic contests, though Mr. Biden has held a steady national lead, helped to a great degree by divisions on the left.
The rupture has the potential to anger supporters of both Ms. Warren and Mr. Sanders, heighten Democratic anxieties about diversity and bigotry in the 2020 election, and inject negativity into a still-fluid race in Iowa, where Democrats often reward positive behavior from presidential candidates.
“I think you called me a liar on national TV,” Ms. Warren told Mr. Sanders after the debate, 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, Mr. 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.”
Ms. Warren replied, “Anytime.”
“You called me a liar,” Mr. Sanders said. “You told me — all right, let’s not do it now.”
Tom Steyer, the billionaire businessman, approached Mr. Sanders in the middle of the exchange.
“I don’t want to get in the middle,” Mr. Steyer said. “I just want to say, ‘Hi, Bernie.’”
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 Ms. Warren and Mr. Sanders share an ideological cause, up to a point, they cannot ultimately share a presidential nomination. In Des Moines, the dream of the left, that both of them could compete to the end without ever clashing in a way that might damage either, was exposed as a fanciful aspiration.
But for that dream to break down amid allegations of sexism and mendacity could be a particularly perilous demise. For Ms. Warren, taking on Mr. Sanders face-to-face risked further enraging the far left, loud sections of which have already turned on her bitterly for her rivalry with Mr. Sanders. And while Ms. Warren appeared to win a positive reception for addressing the subject of gender head-on during the debate, even Democrats supportive of her campaign acknowledge that so prominently tackling sexism could risk leaving timid primary voters uneasy about the implications of nominating a woman.
The rift has already roiled progressives, who fear the public division will benefit the moderates in the race — and, more broadly, threatens the movement they have tried so hard to build. Leading progressive groups spent hours Wednesday trying to craft joint statements of unity among themselves while their leading political figures were in the most bitter public fight of their professional lives.
“I am hoping that volunteers and grass-roots 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 Mr. 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 Representative Richard A. Gephardt of Missouri and former Gov. Howard Dean of Vermont helped the more moderate Senator 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 Mr. Dean after his unsuccessful primary run.
For Mr. Sanders, there is little upside to a drawn-out clash with Ms. Warren, particularly over matters of gender and sexism. While Mr. Sanders’s hard-core base has rallied to his side, much of the Democratic electorate still harbors feelings of resentment toward Mr. Sanders for his conduct toward Hillary Clinton during the 2016 presidential primaries. For him to be accused now, by one of the party’s most prominent women, of mounting an attack on her honesty could revive those grievances and narrow Mr. Sanders’s already tenuous path to winning acceptance from voters closer to the middle.
And in a conflict heavily focused on which candidate is telling the truth, Ms. 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 Ms. Warren is lying, it is likely to hurt her more than it would hurt Mr. Sanders if voters concluded that he was lying.
It is unclear whether either candidate might be inclined to perpetuate the feud in public. It is telling that Ms. Warren’s most pointed comment to Mr. Sanders came after the formal debate concluded, and that Mr. Sanders responded not by escalating the fight but by deferring it to another time.
Still, the last few days may already have taken a severe toll on the prospect that either Mr. Sanders or Ms. Warren might emerge from the primaries as a unity candidate of the left, with the weaker of the two yielding to the stronger after the first few rounds of voting. At the moment, there is little evidence that either is inclined toward that kind of self-effacing ideological solidarity.
Both the Warren and Sanders campaigns declined to comment on Wednesday. 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.
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 Mr. Sanders and Ms. Warren had been wearing onstage.
Over the weekend, Ms. Warren said she was “disappointed” in Mr. 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 Mr. Sanders had told Ms. Warren in a private meeting in 2018 that he thought a woman could not win the presidency; Mr. Sanders vehemently denied it.
“I thought a woman could win; he disagreed,” Ms. 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,” Mr. Sanders insisted, about her characterization of his 2018 remarks. Ms. 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, Mr. 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.”
Reid J. Epstein and Sydney Ember reported from Des Moines, and Alexander Burns from New York. Reporting was contributed by Michael M. Grynbaum and Astead W. Herndon from New York, and Lisa Lerer from Washington.