Following Monday’s acrimonious exchanges between Senators Bernie Sanders and Elizabeth Warren, the leader of one left-wing activist group summed up the sudden breach between the two liberal presidential candidates with an analogy on Twitter: “Mom and dad are fighting and all I wanna do is go to my room and put my headphones on.’’
For a year, Mr. Sanders and Ms. Warren have refused to criticize each other in the 2020 race, instead directing their attacks at moderate candidates and President Trump. But on the eve of Tuesday night’s Democratic debate in Des Moines, and just three weeks before the Iowa caucuses, Ms. Warren on Monday confirmed a news report that Mr. Sanders told her in a meeting in 2018 that a woman could not win the presidency. Mr. Sanders strongly denied he said that.
The back-and-forth was not only the most serious schism between the two in the primary race, but it has also split supporters of the candidates — the most vehement of whom have used the episode to rehash old fights. The controversy has also prompted activist groups who view Mr. Sanders and Ms. Warren as their standard-bearers to lament a disruption that could provide an advantage to the party’s moderate candidates.
Waleed Shahid of the progressive group Justice Democrats said he was “saddened” by the conflict and viewed it as a distraction from the goal of overtaking the centrist front-runner, former Vice President Joseph R. Biden Jr.
“Biden remains in the lead nationally with numerous vulnerabilities that have yet to be adequately vocalized by the candidates,” Mr. Shahid said.
Amid the tumult, other prominent liberal leaders have another message: Calm down and move on, and have both candidates and their supporters focus on working together to defeat the party’s moderate wing.
“We have an opportunity to defeat the corporate wing of the Democratic Party, and that’s where this primary should be focused,” said Charles Chamberlain, who leads the left-wing group Democracy for America. “This helps no one.”
There is also fear among liberals that the dispute would become a focal point of Tuesday’s presidential debate — the last one before the Feb. 3 caucuses. At previous debates, Ms. Warren and Mr. Sanders have made a point of remaining political allies, even as some differences have emerged on issues such as health care.
In polls, the combined voter support for Ms. Warren and Mr. Sanders has represented a plurality that is larger than Mr. Biden’s support for months. But many on the left worry that, despite the comity that characterized much of their interactions with each other in 2019, the zero-sum nature of the primary would eventually force each camp to try to undermine the other’s support at the ballot box.
The latest episode has only deepened those concerns, capping what has been weeks of growing internal tensions. Those in Ms. Warren’s orbit have been frustrated by repeated attacks from the decentralized, ideologically rigid universe of Mr. Sanders’s online supporters; some of them have framed Ms. Warren as inauthentic and disingenuous since she released a health care plan that differed from Mr. Sanders’s “Medicare For all” vision. These attacks have included efforts that her supporters have said were sexist, including one viral tweet that made fun of Ms. Warren dancing at a recent rally in New York City.
The tension heightened on Sunday when Ms. Warren said she was “disappointed” in Mr. Sanders after reports that his campaign distributed an organizing script to volunteers instructing them to portray Ms. Warren as elite and out of touch. It continued Monday when CNN reported that Ms. Warren had told people that in a private 2018 meeting Mr. Sanders told her a woman could not win the presidency. Other news organizations, including The New York Times, soon confirmed the report.
Mr. Sanders denied the accusation, saying instead that he had told Ms. Warren that President Trump would be unforgiving in his attacks on a female candidate. Ms. Warren issued a brief statement Monday night asserting that her friend and rival had in fact told her a woman could not win.
In this instance and the one with the volunteer script, supporters of Ms. Warren said she was not the instigator of conflict.
“I don’t think this is what Warren wanted to be talking about today,” said Maurice Mitchell, the national director of the Working Families Party, which has endorsed Ms. Warren. “Friends don’t always agree but we believe that Warren and Sanders have far more that unites them — and not just them but their supporters. We think their supporters should focus their fire on the corporate wing of the Democratic Party.”
“A Bernie-Warren battle doesn’t do Bernie or Warren any good,” he went on, “nor our bases, nor our movement. There is a whole corporate wing of the Democratic Party we need to defeat.”
Whoever finishes ahead of the other on the night of the Iowa caucuses will seek to claim the mantle of progressive front-runner, which could have a significant impact on their path to the nomination. Liberals have quietly worried about the acrimony that could surface that evening, if the supporter base of one candidate loudly calls for the other to drop out. Other leaders, who see Mr. Sanders’s and Ms. Warren’s electorates as more distinct, say both candidates will be in contention through the Super Tuesday contests in March.
“This will be a long primary,” Mr. Chamberlain said.
But as the events of the last few days make clear, tensions are growing. And while some dismissed Monday’s war of words as a media-concocted feud, others affiliated with Mr. Sanders accused Ms. Warren’s team of a cynical political move to imperil his reputation.
Early Tuesday morning, Mr. Sanders’s campaign released a new television advertisement focused on his record defending women’s rights. The spot, called “On Our Side,” contrasts Mr. Sanders’s record with Mr. Trump’s. RoseAnn DeMoro, a former leader of the nurses union who is close to Mr. Sanders, said Ms. Warren was making a political play that would backfire.
“I find it unfathomable that she would believe that attacking Bernie Sanders with a lie that he essentially disrespects women — which is just outrageous — would pull the female support toward her,” Ms. DeMoro said. “Women aren’t that shallow.”
“I don’t believe she honestly believes at this stage in the game she can win,” she said.