NEW YORK (AP) — CNN is drawing fire from Bernie Sanders supporters for a debate moderator's question that appeared to dismiss his denial of a story that he had told rival Elizabeth Warren that a woman couldn't win the presidential election.

The issue, first raised in a story reported by CNN earlier this week, became a part of CNN's coverage Tuesday of a debate between Democratic presidential candidates co-sponsored with the Des Moines Register.

Sanders was pressed by CNN political correspondent Abby Phillip, one of the debate moderators, who asked him: “I want to be clear here. You're saying that you never told Senator Warren that a woman could not win the election?”

“That is correct,” he replied.

She then turned to Warren and asked, “What did you think when Senator Sanders told you that a woman could not win an election?”

There was some laughter from the audience, and Sanders shook his head.

It was an odd moment: Phillip, a veteran of the Washington Post, ABC News and Politico, was appearing to dismiss Sanders' denial or imply that it was not believable. The fact that CNN broke the initial story about the alleged conversation between the candidates, first based on anonymous sourcing but then confirmed by Warren, added another layer of intrigue.

It provoked anger among Sanders supporters on Twitter, one of whom wrote that fellow fans of the Vermont senator should tweet to CNN “and let them know just how bad and unreasonable” its work on the debate had been.

The Poynter Institute, a journalism think tank, wrote Wednesday that it was a stunning moment — “stunning it its ineptness, and stunning in its unprofessionalism.”

Phillip's question to Warren “was tantamount to calling Sanders a liar, and that certainly should not be a moderator's job, especially when Philip had the opportunity to ask Warren directly if Sanders ever told her that," Poynter said. "If Warren said yes, then and only then should Phillip have asked what Warren thought.”

CNN on Wednesday would not comment publicly on the question.

Warren went on to make one of her most-quoted statements of the night, noting that she and fellow candidate Sen. Amy Klobuchar had won all of their elections while the men on stage hadn't.