The confirmation battle over Supreme Court nominee Neil Gorsuch is off and running, and opponents already know he’s superbly qualified with a fine judicial temperament. But Democrats are still itching for a fight, and their first line of offense is the myth of the “stolen” seat.

“This is a seat that was stolen from the former President, Obama, that’s never been done in U.S. history before,” declared Oregon Senator Jeff Merkley in announcing that he will attempt to filibuster Judge Gorsuch. “To let this become normal just invites...