I still think Comey is an honest man. But his memoir is a big mistake.

Up until now, Comey has been a devastating witness against Trump because, unlike the president, he is so obviously upright and so careful in what he has said. He sounded truthful when he testified under oath that Trump tried to extract a loyalty oath from him and asked him to go easy on disgraced national security adviser Michael Flynn. But Comey is now undercutting his own standing as an impartial avatar of justice by giving into the temptation to tell the world what he really thinks of the president who fired him.

Comey should remember that revenge is a dish best served cold. By heating up his dispute with the president prematurely, he is potentially undercutting the work of another former FBI director who is now investigating the president. Special counsel Robert S. Mueller III has been smart enough to keep his own mouth shut: He hasn’t said one word for or against Trump in public. But now Trump will try to unfairly tar him as a “friend” of Comey’s who must be pursuing a political vendetta against him.