Never Call a State Where People Are Still Voting

The Associated Press and other media outlets interfered in the election last night in Iowa by calling the state for Trump while Iowans were still casting votes in the caucus. Trump’s win wasn’t close, so any effect was on the margins. But that’s no defense. It’s happened before; there are predictable ways to avoid doing it, which were ignored; and there are real reasons to worry about the destabilizing effects in this climate if it happens again in a closer election.

The caucus began at 7 p.m. Central, 8 p.m. on...