Secretary of Defense James Mattis did the honorable thing on Thursday and resigned — in contrast to one of his predecessors, Robert Gates, who left the Obama administration quietly and then wrote a book bashing his boss.

Beltway pundits are in a collective freakout, as the “adult supervision” theory of Donald Trump implies he cannot govern by himself.

Still, Mattis’s resignation letter was noteworthy for one fact: how little it said about defense.

In a page-and-a-half of argument, Mattis barely mentioned his core responsibility at the Pentagon, except to say — twice, and in exactly the same way: “we must use all tools of American power to provide for the common defense.” In other words: national security depends on multilateralism.

Earlier this month, Secretary of State Mike Pompeo gave a speech arguing exactly the opposite: that sometimes multilateralism thwarts American security and interests.

Mattis described a common effort to push back Russia and China — leading the Trump-hating media to speculate that he was accusing the president of doing our enemies’ bidding. But as Pompeo argued, China and Russia have exploited weak multilateralism to advance their own interests.

Trump’s position is that the U.S. can best confront rivals and help allies when placing its national interest, and the nation-state model, at the core of foreign policy.

Not surprisingly, someone who sees multilateralism as the priority, which Mattis suggests he does in his letter, would have trouble hanging on in a Trump administration. He and the president agree on two things: the defense department is in better war-fighting shape than it was before, and the U.S. must confront China and Russia.

The disagreement is about means, not ends. The only damage to national security, if any, came from the media’s panic.