Tensions between 2020 Democratic presidential candidates, Sen. Elizabeth Warren (D-Mass.) and Sen. Bernie Sanders (D-Vermont), escalated on Monday as Warren alleged that Sanders made a misogynist comment that a woman could not win the 2020 election.

Warren claimed that Sanders told her in a private meeting in December of 2018, that he did not think a woman could win the 2020 presidential race. The controversial accusation, which Sanders had previously denied in a CNN report, undermines the undeclared peace pact between the long-term friends.

The two-person meeting took place at Warren’s apartment in 2018.

The pair agreed that while vying for the presidential bid it would be in each other’s best interest not to personally attack one another for fear of undermining the progressive movement. The two also discussed the best method to take on President Donald Trump. Warren laid out two reasons she believed that she made a promising candidate – she could conduct a robust argument about the economy and earn widespread support from female voters.

Sanders allegedly responded in the friendly gathering that he did not believe that a woman could win.

Warren’s accusation has created a schism between the two front-running liberals vying for the presidential nomination. It also significantly raised the tensions surrounding the six candidates before the final debate before the caucuses to be held in Des Moines, Iowa, on Tuesday night.

Sander’s senior adviser Jeff Weaver suggested in an interview with CNN that Warren had misconstrued Sander’s comments.

“Among the topics that came up was what would happen if Democrats nominated a female candidate,” Warren said in response to questions about the December 2018 meeting on Monday night.

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“I thought a woman could win; he [Sanders] disagreed.”

Four sources had previously told CNN that Sanders made the statement to Warren in their friendly meeting.

Sanders denied the allegations in a statement to CNN, claiming that it was “ludicrous to believe that at the same meeting where Elizabeth Warren told me she was going to run for president, I would tell her that a woman couldn’t win.”

“It’s sad that, three weeks before the Iowa caucus and a year after that private conversation, staff who weren’t in the room are lying about what happened. What I did say that night was that Donald Trump is a sexist, a racist and a liar who would weaponize whatever he could,” Sanders stated. “Do I believe a woman can win in 2020? Of course! After all, Hillary Clinton beat Donald Trump by 3 million votes in 2016.”