Bernie Sanders once told Elizabeth Warren that he didn't think a woman could win in 2020: report

It would appear that the pre-Iowa tensions between 2020 progressive candidates Bernie Sanders and Elizabeth Warren are heating up following the release of a news report about a private conversation the two reportedly had just over a year ago.

On Monday afternoon, CNN broke a story saying that Sanders told Warren during a December 2018 private meeting that a woman couldn't win the presidential race. The two had met to discuss the possibility of running against each other in a Democratic primary:

The two agreed that if they ultimately faced each other as presidential candidates, they should remain civil and avoid attacking one another, so as not to hurt the progressive movement. They also discussed how to best take on President Donald Trump, and Warren laid out two main reasons she believed she would be a strong candidate: She could make a robust argument about the economy and earn broad support from female voters.

Sanders responded that he did not believe a woman could win.

The description of that meeting is based on the accounts of four people: two people Warren spoke with directly soon after the encounter, and two people familiar with the meeting.

Sanders, however, says that CNN's sources weren't telling the truth and that he didn't say what he's been accused of saying and that a woman can win the election:

"It is 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," Sanders told the outlet. "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. Do I believe a woman can win in 2020? Of course! After all, Hillary Clinton beat Donald Trump by 3 million votes in 2016."

As to Warren's take on the story, her campaign declined to comment on it, which is significant because — since she was reportedly in the room — her weighing in on the matter could refute the claim instead of allowing it to continue playing out in the news cycle, as Axios' Jonathan Swan pointed out.

This story comes on the heels of an exchange over the weekend where Warren criticized Sanders for "sending his volunteers out to trash me," after Politico reported that Sanders' campaign volunteers had been using talking points to paint Warren as a candidate of the wealthy who is "bringing no new bases into the Democratic Party."

The apparent escalation between the two far-left candidates comes just ahead of Tuesday's Democratic National Committee primary debate — which will be the last such event before the Feb. 3 Iowa caucuses — meaning there's a chance that the two senators could end up swapping some televised blows on stage. With only six candidates qualifying, the debate will be the smallest such event yet.

Sanders is currently polling ahead of Warren overall, with both of the candidates still trailing behind former Vice President Joe Biden, according to RealClearPolitics' averages on Monday.

Meanwhile, on Monday, the progressive political action committee Democracy for America urged the two to de-escalate things between them and focus their energies on less-progressive Democrats, tweeting "you both are progressive champs & our movement needs to see you working together to defeat your corporate Dem opponents — not attack each other."