Mr. Trump doesn’t understand, or perhaps doesn’t care, that all of this hurts Mr. Barr, whom he can ill-afford to lose. The AG is smart, tough and independent. He will give Mr. Trump his candid advice on the law, which is more than most of his advisers do. Mr. Barr finally spoke up in frustration about this Thursday, telling ABC News that Mr. Trump’s outbursts are making it “impossible for me to do my job.”

The President should listen because he needs Mr. Barr more than Mr. Barr needs to be AG. The danger for Mr. Trump is that Mr. Barr will resign because he is tired of having his credibility undermined by a President who can’t control his political id no matter the damage it causes.

Mr. Trump won’t like to hear any of this, and no doubt his loyalists will blame Democrats, the media and Mr. Barr. But Mr. Trump is his own worst enemy. Time and again his need to dominate the news, to justify even his mistakes, and to rebut every critic gets him into needless trouble.