“I didn’t cook up a convenient tradition here,” he said. “You don’t endanger the country by attacking the elected commander in chief. I may not like a commander in chief one fricking bit, but our system puts the commander in chief there, and to further weaken him when we’re up against real threats—I mean, we could be at war on the Korean peninsula, every time they start launching something.”

The subject of North Korea represented my best chance to wrench a direct answer from Mattis. I had collected some of Trump’s more repellent tweets, and read aloud the one that I thought might overwhelm his defenses. It is a tweet almost without peer in the canon…

Mattis looked at his hands. Finally he said, “Any Marine general or any other senior servant of the people of the United States would find that, to use a mild euphemism, counterproductive and beneath the dignity of the presidency.”…

I thought back to what he’d told me earlier in the summer, when I had asked him to describe something Trump could say or do that would trigger him to launch a frontal attack on the president. He’d demurred, as I had expected. But then he’d issued a caveat: “There is a period in which I owe my silence. It’s not eternal. It’s not going to be forever.”