Secretary of Defense James Mattis has been eased out of President Trump’s inner circle, and no one should be surprised, though we all should be alarmed.

The shove-aside—reported by NBC News on Monday and confirmed to me by two inside sources—has been in process at least since May, when Trump announced his withdrawal from the Iran nuclear deal without notifying, much less consulting, Mattis. But this decline in status was probably inevitable.

Trump hired Mattis, a retired Marine four-star general and decorated combat commander, on a false premise from the start. Having heard that his nominee was known in some circles as “Mad Dog Mattis,” Trump figured that he’d be getting a savage killer keen on torture. “We’re going to put in the greatest killers of all time,” Trump bragged at a post-election rally where he announced some of his Cabinet picks.

Mattis hates the nickname, which few if any colleagues actually used, and it’s certainly misleading. He did once famously tell the troops he commanded in Iraq, “Be polite, be professional, but have a plan to kill everybody you meet”—but the first part of that injunction is as important as the second part. His peers have called him “Warrior Monk,” referring to the fact that he’s never married and reads deeply in history, philosophy, and strategy, and possesses a library of some 7,000 volumes. In Iraq, he carried a copy of Marcus Aurelius’ Meditations in his rucksack.

In short, yes, Mattis is a killer—he was, after all, a Marine commanding general in wartime—but he’s also an intellectual, even contemplative. In one of their first meetings, Trump asked Mattis what he thought of waterboarding. Mattis said he could get more information from a detainee with “a pack of cigarettes and a couple of beers.” Trump said later that he was surprised by this answer but ceded to Mattis on the issue—and on nearly every other issue where Mattis weighed in.

That was the pattern of Trump’s first year in office: The president deferred to the men he called “my generals” and particularly to the ex-general turned defense secretary, in part because he assumed that the big problem with U.S. foreign policy was that President Obama had ignored the generals—and perhaps in part because he realized he didn’t know much about the subject and so figured that relying on the generals would set him straight.

However, in recent months, Trump has grown into his job—or thinks he has—and appears more confident in his own judgment on foreign policy. This self-confidence took a big jump after he fired Secretary of State Rex Tillerson and national security adviser H.R. McMaster—whose views he rarely shared and whose styles he didn’t like—and replaced them with Mike Pompeo, who had cultivated close ties with Trump as CIA director, and John Bolton, a longtime hawk whose commentary on Fox News appealed to Trump’s instincts.

After firing Tillerson, Trump told reporters, “I’m really at a point where we’re getting very close to having the Cabinet and other things that I want.” Bringing on Bolton to replace McMaster seems to have brought him closer still. Is Mattis the next one to go?

In recent months, Trump has grown into his job—or thinks he has—and appears more confident in his own judgment on foreign policy.

Clearly Mattis has been only peripherally involved, if that, in some of Trump’s most recent foreign policy moves: the summit with North Korean leader Kim Jong-un; the cancellation of joint U.S. military exercises with South Korea (another decision made without consulting him); the upcoming summit with Russian President Vladimir Putin; the move of the U.S. embassy in Israel to Jerusalem (contrary to Mattis’ advice); and the proposal to create a separate service for military operations in outer space (which Mattis had opposed in a letter to Congress).

Mattis has taken care to establish good relations with the new members of the national security team. He’d spoken regularly with Pompeo in his time at CIA and still does. He had never worked with Bolton, and had advised Trump not to hire him (another case where his view was ignored), but once the deed was done, he struck up good relations. On Bolton’s debut visit to the Pentagon, Mattis greeted him on the steps and said, “I heard you’re actually the devil incarnate, and I wanted to meet you.” Bolton laughed.

Still, the dynamics are very different from the time when Mattis, Tillerson, and White House chief of staff John Kelly formed an effective triumvirate. In the early months of Trump’s presidency, Mattis and Kelly agreed not to travel abroad at the same time, so that at least one of them could monitor—and if necessary, block—orders and edicts from the White House. (Kelly’s role of gatekeeper has also since greatly diminished.)

Essentially, Mattis is a foreign policy traditionalist. He believes in alliances (especially NATO), treaty commitments, free trade, and diplomacy; he distrusts Russia, mainly because Putin aims to diminish the appeal of democracy and undercut the Western alliance. Trump disagrees on all these points. When Cabinet secretaries—especially secretaries of state or defense—are so out of step with the president, their days in office are usually numbered, not least because foreign leaders can no longer assume their views reflect those of the commander in chief.

In many foreign capitals, and also here at home, Mattis is widely viewed as the last of the grown-ups in the Trump administration. (Kelly has surrendered to Trump’s demands and desires so thoroughly that he’s long ago been dropped from the category.) Some leaders, in allied nations and on Capitol Hill, refer to the Department of Defense under Mattis as “the Department of Reassurance,” for all the times Mattis has reassured them that the United States will still uphold some commitment or another, regardless of what Trump had tweeted or said.

Not long ago, many regarded Mattis as nearly invincible because, if he resigned or was fired, the allies would panic and even Republicans in Congress might turn against the president, finding the prospect of Trump-without-Mattis as too dangerous to bear. This perception gave Mattis great leverage. But now, the allies are panicking already—and congressional Republicans, seeing colleagues lose primaries when they criticize Trump at all, are proving themselves incapable of turning against him, whatever the peril.

If Trump is “very close to having the Cabinet and other things that I want,” will he finally have it after Mattis leaves? And what, one almost shudders to ask, are those “other things”?