House Speaker Nancy Pelosi on Tuesday endorsed an official inquiry to impeach President Trump, and there is joy across Resistance America—at least for now. The decision guarantees that this will go down as the Impeachment Congress, with little to show beyond investigations into the Trump campaign and now the Trump Presidency.

In one sense this moment was probably inevitable. Most Democrats and most of the media have never accepted Mr. Trump as a legitimate President. They can’t believe 63 million Americans voted for him over...