The House Democratic impeachment inquiry is unserious. Yes, it is a solemn moment whenever the House considers a resolution calling for a president’s removal from office. But the frivolous manner in which Democrats are proceeding shows they believe that given what we know now, they can’t create a bipartisan consensus for removing President Trump.

Polling savants and communications gurus must be feeding Speaker Nancy Pelosi and her team key phrases. She announced the inquiry by castigating Mr. Trump for “betrayal of his oath...