It’s the fourth quarter. The game is close. And you are benched.

That could sum up the frustrations of four senators — two of them front-runners for the Democratic presidential nomination — who will be duty bound to leave the campaign trail next week to sit in judgment of President Trump.

The Senate impeachment trial is expected to begin as early as Jan. 24, less than two weeks before the all-important Iowa caucuses.

With members of the Senate serving as official jurors who will determine Mr. Trump’s guilt or innocence, three participants in Tuesday’s debate, Amy Klobuchar, Bernie Sanders and Elizabeth Warren, must head back to Washington in the midst of the campaign.

That will leave little time for stumping in Iowa.

Ms. Warren, who is regarded as one of the top four contenders in the race, has voiced her concern over leaving the campaign trail. Asked during Tuesday’s debate how big a problem her absence will be, she vowed to return to Washington.