President Trump has gradually discovered the meaning of the oath he swore on Jan. 20, and he doesn’t seem to like it. In the course of an interview on “The Larry O’Connor Show” last week, he said, “The saddest thing is that because I’m the president of the United States, I am not supposed to be involved with the Justice Department. I am not supposed to be involved with the FBI. I’m not supposed to be doing the kinds of things that I would love to be doing. And I’m very frustrated by it.”

Meet James Madison’s Constitution,...