An angry split among liberal Democrats broke into the open Wednesday as two prominent presidential candidates exchanged accusations of dishonesty, raising fears among party leaders of a repeat of the internecine bitterness that many Democrats say contributed to President Trump’s victory in 2016.

The dispute simmered all day between Sens. Bernie Sanders (I-Vt.) and Elizabeth Warren (D-Mass.) over whether he had told her that a woman cannot win the presidency. Social media users identifying themselves as Sanders supporters used snake icons to symbolize Warren’s ostensible duplicity, played up her Republican roots and circulated a #Never­Warren hashtag.

Warren’s backers, while taking a less aggressive tone, nonetheless revived questions of whether many of Sanders’s supporters are sexist and whether he contributed to the party’s disastrous 2016 loss with a display of self-centered petulance.

The clash intensified when CNN released audio Wednesday evening of a sharp exchange between the two that unfolded following Tuesday’s Democratic debate. “I think you called me a liar on national TV,” Warren can be heard saying. Sanders replies: “You know, let’s not do it right now. If you want to have that discussion, we’ll have that discussion.”

Warren then says, “Anytime.” That prompted Sanders to respond, “You called me a liar. You told me — all right, let’s not do it now.”

Increasingly alarmed liberal leaders scrambled to make peace. “Many of the voices in the progressive community are warning we cannot have a knife fight in a phone booth, or a circular firing squad,” said Randi Weingarten, president of the American Federation of Teachers.

That message, she said, is being sent to the Sanders and Warren camps “privately and publicly.”

The two senators have been circling each other warily for more than a year — each seeking to woo rather than alienate the other’s voters — as many in the party remain traumatized by the 2016 feud between Sanders and Hillary Clinton.

This time, the Democratic presidential contenders have largely kept the peace — until now, with less than three weeks to go before the Iowa caucuses on Feb. 3.

Warren, during Tuesday’s Democratic debate, repeated her assertion that in a 2018 private conversation, Sanders told her a woman could not win the White House; he again forcefully denied it. But while the two were cordial during the event, Warren afterward avoided shaking Sanders’s hand, and they appeared to have a testy exchange, providing more grist for Wednesday’s back-and-forth.

It was clear the exchange was heated, but it wasn’t known what it entailed until CNN, which had sponsored the debate, released the audio in the evening.

All day, Republicans, seeing an opportunity, sought to stoke the Democratic hostility. President Trump weighed in on Sanders’s side, much as he had egged on Sanders’s supporters in 2016.

“I don’t know him, I don’t particularly like him, he’s a nasty guy — but I don’t believe he said this,” Trump said at a rally Tuesday night.

Even relatively centrist Democrats worried about the potential for vitriol to disrupt the party’s ability to defeat a president they consider toxic. “We can’t have it,” said former Virginia governor Terry McAuliffe. “People want to beat Trump, and I do think that is a motivating factor for all of us to come together.”

He added, referring to the hard-fought Democratic primary contest, “I hope it doesn’t go on too long.”

Both campaigns had telegraphed a desire to de-escalate tensions in the hours before Tuesday’s debate, making the exchange between Sanders and Warren all the more striking.

Asked earlier Wednesday what the two were talking about, Sanders quipped to an MSNBC reporter, “the weather.”

Representatives for the Warren campaign declined to comment.

After the two candidates separated Tuesday night, they both shook hands with other candidates — Warren with former South Bend, Ind., mayor Pete Buttigieg and Sanders with billionaire businessman Tom Steyer.

Steyer, who found himself between Warren and Sanders as they spoke, told MSNBC’s Chris Matthews that he did not know what they had said to each other.

“All I was trying to say, to both Senator Warren and Senator Sanders, was, ‘It’s great to see you, thank you for participating in this.’ And whatever they were going on with each other, I was trying to get out of the way as fast as possible,” said Steyer.

After the content of Warren and Sanders’s exchange became public and started ricocheting across social media, Sanders aides took to Twitter urging supporters to not divert their attention from the issues the senator has championed throughout the campaign.

“Tonight, half a million people will sleep on the streets in the richest country in the world,” wrote Bill Neidhart, a top Iowa staffer for the Sanders campaign. “Stay focused.”

Throughout the day, the rift between the two liberal candidates was amplified on social media, where an outpouring of anti-Warren sentiment stoked fears of a replay of 2016, when intraparty divisions were exploited by Russian actors aiming to boost then-candidate Trump.

Snake emoji flooded the comment sections under Warren’s recent tweets and Instagram posts. The privacy settings of commenting accounts often obscured their identity, making it unclear who they were and whether they were even based in the United States.

No similar online crusade seemed to take shape against Sanders, even as his supporters decried his treatment by the moderators of Tuesday’s debate in Des Moines and his subsequent reception on cable news.

On Twitter, #NeverWarren and #WarrenIsASnake began trending — reprising labels that have been used since at least July. (A trending hashtag does not indicate that users widely agree with it but rather that it is being broadly discussed, including by some who may strongly object to the label.)

The anti-Warren epithets also gained traction among pro-Trump activists who organize around the president’s “Make America Great Again” rallying cry. “#NeverWarren,” wrote one user with “Cult 45” in her bio. “Never any Democrat!”

Conservatives with large followings, such as representatives of Turning Point USA, which trains students to undertake conservative activism, also joined in to promote the anti-Warren attacks.

The speed with which conservatives seized on the rift alarmed liberal activists, who warned Democrats not to play into Republican hands.

“I think that people who support Sanders or Warren should refrain from going to battle with each other,” said Charles Lenchner, a co-founder of the “People for Bernie” campaign. “This should be true even if staffers or principals or surrogates make the mistake of feeding into that conflict.”

Some supporters of the two candidates tried to tamp down the flames. “We saw what was happening yesterday and the day before that and the day before that,” said Nina Turner, a national co-chair for Sanders’s campaign. “You don’t need me to enumerate it. All I’m saying is, sometimes good folks do bad things. We have to make sure we don’t fall into these traps.”

That echoed Sanders himself, who at Tuesday’s debate said, “I don’t want to waste a whole lot of time on this because this is what Donald Trump and maybe some of the media want.”

Turner was joined at an event in Iowa on Wednesday by Cornel West, another of Sanders’s surrogates. “It’s about solidarity and integrity,” he said on his way out of the event.

Adam Green, a Warren ally and co-founder of the Progressive Change Campaign Committee, tried to minimize the tense moment onstage, saying that “most actual voters” do not care about whether there is a personal rift between the senators.

“Some pundits, bored with issues that voters care about, are focusing on the exit from the stage that impacts zero people’s daily life,” Green said.

But in Iowa on Wednesday, voters were still chewing over the events of the past few days and seemed eager to share their opinions.

Trevor Golnick, a sophomore at Iowa State University who plans to caucus for Sanders, said he wasn’t sold on Warren’s account of the 2018 meeting. “I think it was really disingenuous, personally,” he said.

“Seeing her body posture and the way she reacted — she didn’t seem very honest, in my opinion,” he said. But Golnick said he would vote for Warren if she is the nominee.

Iowans watching TV after the debate, however, saw late-night host Stephen Colbert take a shot at Sanders enthusiasts and suggest they are sexist.

“If you want to see Bernie say nice things about female presidential candidates, go to YouTube,” Colbert said during his opening monologue on CBS’s “Late Show” on Tuesday night. “If you want to see his supporters saying terrible things about them, go to the comments section.”

In Washington, some Democratic lawmakers and strategists privately fretted over the dispute Wednesday, worrying that it would divide the party and create new fissures on the left.

One top Democrat who knows both candidates said Warren and Sanders have more in common than any other pair of prominent contenders, presenting both advantages and drawbacks for the respective roles in the race.

Others explained the raw moment as an unscripted glimpse into the candidates’ emotions, which are running high as the campaign approaches a moment of truth when voting actually begins.

“It’s hard to project an image of unity a couple of weeks before the Iowa caucuses and the New Hampshire primaries,” said Rep. Jamie B. Raskin (D-Md.), who is preparing to endorse Warren.

“It was obviously a tense moment,” Raskin said. “I’ve spoken to a number of members of Congress today who want to be sure the rivalry is robust and uninhibited, but it doesn’t lead to the kinds of bruised feelings and burned bridged that took place in 2016.”