Partisans will keep lining up for or against impeachment. What should worry Democrats is that independents increasingly agree with Republicans on the question—and these are the swing voters likely to decide the White House in 2020.

Yet House committee chairmen won’t stop trying to oust Mr. Trump. Reps. Jerry Nadler (Judiciary), Adam Schiff (Intelligence), Elijah Cummings (Oversight) and Maxine Waters (Financial Services) will keep issuing demands and subpoenas. The country will have to put up with endless hearings built around five minutes of questions of varying quality by mostly forgettable members of Congress, punctuated by a few moments of drama.

The possibility of removing Mr. Trump from office, a prospect that enthuses one party’s true believers and enrages the other’s, will hang over the proceedings. But remember, the independent voters whose ballots will decide the 2020 election are losing patience.

There’s worse news for Democrats. These Trump investigations will dominate the headlines, obscuring efforts by House Democrats to project a positive agenda on the economy, health care, student loans, gun control, election reform and other themes that Speaker Nancy Pelosi desperately wants to play up going into the election.