White House aides hope the process will wrap up by the State of the Union address on Feb. 4, the day after the Iowa caucuses. But top Senate Republicans have indicated that they expect the trial could easily extend past then, running into the New Hampshire primary and maybe even beyond if the Senate votes to call witnesses.

The campaigns are trying to make the best of a bad situation, chartering planes for middle-of-the-night flights back to Washington and organizing town hall events hosted via phone or video chat. Mr. Sanders plans to leverage his social media following by hosting live-stream events. (In the first week of January, Mr. Sanders’s live streams received 6.5 million views, according to his campaign.)

They’re also dispatching top surrogates, like Representative Alexandria Ocasio-Cortez of New York for Mr. Sanders and Representative Ayanna Pressley of Massachusetts for Ms. Warren.

But, of course, supporting cast members can never really replace the star of the show.

The dynamic is probably most damaging to Senator Amy Klobuchar of Minnesota, who lacks the national brands of Mr. Sanders and Ms. Warren and has predicated her success on a strong finish in Iowa, where she is polling in fifth place. Senator Michael Bennet of Colorado, who has less than 1 percent support in the polls, will also be pulled off the campaign trail.

Meanwhile, Mr. Biden and Mr. Buttigieg plan to spend much of the next three weeks in Iowa.

Aides to Mr. Biden say the trial could be an asset, reminding voters that Mr. Trump fears Mr. Biden as a political opponent. (Revelations that Mr. Trump tried to collect political dirt on Mr. Biden and his family from Ukrainian officials kicked off the impeachment inquiry.) They’ve released a new ad arguing that Mr. Trump is “obsessed” with their candidate.

Mr. Buttigieg is planning to spend 15 of the 18 days before the caucuses barnstorming the state.

“I’ll leave it to the analysts to figure out the political impacts,” Mr. Buttigieg said in Iowa on Wednesday. “We’re going to use every moment available to us to continue making the case and to continue listening to voters.”

For Ms. Warren and Mr. Sanders, there might be a tiny sliver of sunshine in all this impeachment doom. The hearings will distract from their escalating — and mutually distracting — feud.