If you’ve followed the Ukraine phone-call news, you might have noticed reality branching into two completely different movies. In one, President Trump was doing his job of protecting the republic by asking an allied country to help out on an important legal investigation. The other movie involves Orange Hitler bullying a foreign country into meddling in our elections by “digging up dirt” on a political opponent.

Which movie is the real one, if such a thing exists? I’d like to offer a rule of thumb for evaluating political...