(CNN) Massachusetts Sen. Elizabeth Warren is done talking about her back-and-forth -- in which each candidate said the other called them a liar -- with Vermont Sen. Bernie Sanders after the seventh presidential debate Tuesday night in Iowa.

"I have no further comment on this," Warren told reporters as she entered the US Capitol for the start of President Donald Trump's impeachment trial on Thursday. "We are here right now at an important moment in American history. And that's what we need to keep our focus on."

And, apparently, Sanders agrees. He ignored questions by CNN reporters on both Wednesday and Thursday as to whether he had anything to say about his confrontation with Warren. Jane O'Meara Sanders, the senator's wife, said only this : "I think that this discussion is over."

Really? Well, it shouldn't be.

Here's why. Sanders and Warren are two of the three or four Democrats with the best chance of winding up as the party's presidential nominee this November. There is an active disagreement between the two over whether, at a meeting in December 2018, Sanders told Warren that he did not believe a woman could be elected president. Warren says he did. Sanders says he didn't.

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