On the eve of the final Democratic debate before the important Iowa caucuses, a private conversation between two of the race’s remaining front-runners has placed one of them in an uncomfortable light.

Four unnamed sources told CNN that, in December 2018, Bernie Sanders told Elizabeth Warren a woman could not defeat President Donald Trump, a charge Sanders vehemently denies.

“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 said in a statement to the network. “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."

Presidential candidate Bernie Sanders recovering after undergoing procedure for blocked artery

Warren's campaign declined comment.

CNN based its story on the accounts of four unnamed sources: two people with whom Warren spoke with directly after the meeting  and two people familiar with the discussion.

Six Democrats — including Warren and Sanders — will take the stage Tuesday night in Des Moines in the final Democratic debate before the Feb. 3 Iowa caucuses. Also on the stage will be former Vice President Joe Biden; former South Bend, Ind., Mayor Pete Buttigieg; U.S. Sen. Amy Klobuchar; and billionaire executive Tom Steyer.

A poll released Friday by The Des Moines Register and CNN found them all with similar levels of support, according to The Associated Press.

For two decades, Iowa has had a solid record of backing the ultimate Democratic nominee. A clear victory in its caucuses next month could set the tone for the races that follow in New Hampshire, Nevada and South Carolina.

Earlier Monday, U.S. Sen. Cory Booker became the latest Democrat to drop out of the race. Booker follows Marianne Williamson last week and Julián Castro earlier this month.

Booker's fellow senator from California, Kamala Harris, ended her bid in early December. Former Congressman Beto O'Rourke dropped out this past October.

Booker was not scheduled to be on stage during the debate.