Hypocrisy is common in Washington, but impeachment is bringing out more than its fair share. That’s true of some Republicans, and the mainstream media devotes countless hours to it. What gets much less attention is the hypocrisy of the party that to which most journalists are sympathetic: the Democrats.

Take Senate Minority Leader Chuck Schumer. On Tuesday he demanded the Senate call witnesses, claiming they’re required for a “fair trial” and slamming Republican opposition as a “coverup.” But the GOP position is exactly what...