Bernie Sanders has a history of questioning the open-mindedness of the country.

Sanders, who's under fire for allegedly telling Elizabeth Warren in 2018 a woman couldn't win the White House in 2020, told the Daily Beast that year that black Democratic gubernatorial candidates Andrew Gillum and Stacey Abrams lost their respective races because of their skin color.

“I think you know there are a lot of white folks out there, who are not necessarily racist, who felt uncomfortable for the first time in their lives about whether or not they wanted to vote for an African American,” the Vermont senator told the outlet.

Sanders and Warren, who have spent a large part of the Democratic primary in policy simpatico, broke a nonaggression pact on Monday after a weekend of simmering tensions.

Warren, 70, slammed Sanders, 78, on Sunday for "sending his volunteers out to trash me" when asked about a leaked Sanders campaign memo encouraging canvassers to question the Massachusetts senator's electability. The campaign argued she only appealed to "highly educated, more affluent people." Sanders denied any involvement in the strategy, calling it a "media blowup."

Then, on Monday afternoon, Sanders supporters accused Warren of leaking a story that claimed he told her he believed a woman wouldn't emerge victorious from a general election against President Trump, during a meeting at her home to advise him that she would seek the White House. Sanders described the story as "lies" and said it was "sad" the anecdote had emerged three weeks out from the Iowa caucuses on Feb. 3.

Warren, however, stood her ground Monday evening, issuing a defiant statement.

"Bernie and I met for more than two hours in December 2018 to discuss the 2020 election, our past work together, and our shared goals: beating Donald Trump, taking back our government from the wealthy and well-connected, and building an economy that works for everyone," she said.

Warren added: "Among the topics that came up was what would happen if Democrats nominated a female candidate. I thought a woman could win; he disagreed."

The feud is set to dominate Tuesday night's debate in Des Moines, Iowa, which is being billed as a platform for the candidates to make their closing arguments before Democrats in the first-in-the-nation state.