Former Secretary of Defense James Mattis, who left the White House last December in the blaze of an extremely passive-aggressive resignation letter, is still smarting over his former boss, Donald Trump, but too sanctimonious to say so. “If you leave an administration, you owe some silence,” Mattis explains to Jeffrey Goldberg in a new interview with the Atlantic. “When you leave an administration over clear policy differences, you need to give the people who are still there as much opportunity as possible to defend the country.”

Of course, Mattis also wants to promote his new book—not subtly titled Call Sign Chaos: Learning to Lead—and unfortunately, Trump is the only thing anyone really wants to talk about. Mattis was one of the so-called “adults in the room” during the early days of Trump’s presidency, along with Rex Tillerson, John Kelly, and others meant to be a moderating influence on a famously immoderate president. A decorated military scholar with more than four decades of service, Mattis has ostensibly written a book about leadership, and his respect for institutions, but it’s impossible not to see the entire enterprise as a repudiation of Trump—a contradiction that Mattis struggles to discuss without violating his own oath to protect the office of the presidency. When Goldberg asks him how he feels about his former boss tweeting his subtle joy that Kim Jong Un called Joe Biden a “low IQ individual,” Mattis just looks 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.”

“Let me put it this way. I’ve written an entire book built on the principles of respecting your troops, respecting each other, respecting your allies. Isn’t it pretty obvious how I would feel about something like that?”

It is pretty obvious, although Mattis remains at pains to avoid elaboration: