And if one of them is to win the nomination, they will likely need significant backing from the other’s supporters eventually, which is why the back-and-forth has freaked out left-wing organizations and activists who see the conflict as a boon to Biden — and insist it’s all in the rearview mirror.

“Both camps are over this and focused on drilling into Iowa voters’ heads that Joe Biden is the least inspirational and least electable nominee we can put forward,” said Stephanie Taylor, the co-founder of the Progressive Change Campaign Committee, a group aligned with the Warren campaign.

But some allies of both campaigns have continued talking about the conflict. “She betrayed him as a friend and showed him that there are no friends in politics,” Ja’Mal Green, a Sanders surrogate and Chicago community organizer, tweeted Thursday in reference to Warren’s decision to not endorse him in 2016. Sanders campaign co-chair Nina Turner hit Warren for her past as a registered Republican and chided her for not shaking Sanders' hand after the this week's debate.

Adam Jentleson, a former Harry Reid aide close to the Warren campaign, wrote on Twitter Wednesday night that Sanders used “doublespeak” to try to deflect Warren’s allegation and retweeted references to “Bernie Bros.”

It shows why fully exorcising the conflict will be more difficult than simply having the candidates proclaim that it’s over. Warren and many on her campaign responded intensely after POLITICO reported that the Sanders campaign had quietly deployed talking points to its canvassers in multiple early states that included language attacking her electability.

The talking points weren’t particularly vicious, but the leaked script struck a raw nerve with Warren and her campaign because they felt they had held up their end of a nonaggression pact with Sanders — even after some Sanders staffers and surrogates had spent most of the race hitting Warren. The Warren campaign got so frustrated about critical tweets and comments from Sanders’ staffers that it privately expressed its displeasure to Sanders campaign manager Faiz Shakir last summer.

But top Sanders aides kept throwing elbows throughout the fall. "There are people who didn't have the same guts and the same courage as Sen. Bernie Sanders to run in 2016. There are some people who sat on the sidelines when it was hard,” Turner, Sanders’ campaign co-chair, said late last year, one of many jabs — some veiled, some not — that Warren allies stewed over, frustrated that Warren world wasn’t hitting back. “There was only one person who stood up to the establishment and his name is Bernard Sanders," Turner continued.

Many in Sanders' orbit, meanwhile, believe Warren’s campaign retaliated by planting a CNN story earlier this week — attributed to anonymous sources, two of whom were described as having talked to Warren afterward — that said Sanders told Warren he didn’t believe a woman could win in 2020. Sanders has denied the charge.

After his on-the-record denial, Warren then issued her own statement backing up the report. “I thought a woman could win; he disagreed,” her statement read.

For some Sanders supporters, grievances they have held against Warren since 2016 — when she stayed neutral in the primary and then pockets of them shouted, “We trusted you! We trusted you!” as Warren gave a speech supporting Hillary Clinton at the Democratic National Convention — then fully spilled out in force.

Some pro-Sanders Twitter accounts have since taken to calling Warren a “snake” and filling her social media with snake emojis, an online tactic that first gained prominence during a fight between Taylor Swift and Kim Kardashian in 2016. It’s unclear whether or how many are bots trying to stoke conflict or Republicans; at least some are professed fans of other Democratic candidates or even people on the right.

And, of course, Thursday’s remarks were not the first time the campaigns had tried to head off potential conflict: Both campaigns signaled to reporters and supporters ahead of Tuesday’s debate that they wanted to cool down the tension and pivot back to their original strategies.

“Bernie is my friend, and I am not here to try to fight with Bernie,” Warren said onstage at the debate.

“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,” Sanders said.

But the two candidates’ accounts of their meeting in December 2018 — when Warren alleges Sanders said a woman couldn’t win in 2020 — are irreconcilable. That fact was highlighted by their post-debate conversation.

"I think you called me a liar on national TV," Warren told Sanders after the debate, according to the audio published by CNN. At first saying they should talk later, Sanders shot back: "You called me a liar. You told me —,” he said before pivoting. “All right, let's not do it now."

Meanwhile, Biden’s allies are happy to keep talking about it. Ex-Vermont Gov. Peter Shumlin, a Biden endorser who introduced the former vice president at a recent fundraiser, slammed Sanders in a Thursday interview with POLITICO, saying he was trying to “Hillarize” Warren.