Thursday's decision by Jim Mattis to leave the stifling, rapidly collapsing confines of Donald Trump’s insane clown posse administration was always inevitable, but that hardly makes the psychological impact of his departure any less traumatic.

In a week with an endless series of body blows to Trump, this one is going to leave a mark. Even with a crashing stock market, the Mueller investigation closing in on Trump’s allies with brutal, inexorable efficiency, his family “charity” exposed as a particularly slimy slush fund, a looming government shutdown, and his failure to deliver his infamous wall to his marks, the Mattis resignation is the Quivering Palm Death Touch.

His extraordinary departure in protest of Trump’s policies and personality is absolutely unprecedented. Mattis naturally objects to the reckless Syria pullout plan, but also to the president’s wholesale abandonment of our traditional allies who have made not only the U.S. but the world safer. As I write this, Washington and the world are reeling, and in deep shock. Even usually Trump-compliant Stockholm Syndrome Republicans in the House and Senate are issuing statements bordering on panic, all while the Trump noise machine warms up to attack Mattis as a Soros shill, a closeted liberal, and a traitor to the Maximum Leader.

Jim Mattis was a talisman for the Washington and international foreign-policy communities, a point of smarts and stability, a ground-wire to short out Trump’s capricious impulses before they could damage America’s interests and values. While never straying from the chain of command, Mattis knew how to work the process, fight back behind closed doors, and maintain relationships with allies and friends around the world.

Even the Trump White House, a hive of the most morally vacant and cowardly bootlicks ever assembled, found themselves relying on Mattis, even if they never trusted him. If Trump ever realizes how much his own White House staff counted on the Marine general turned SECDEF to control his impulsive defense and foreign-policy decisions, he’ll have a Twitter stroke.

I can’t tell you the number of times I’ve had Republican representatives and senators whisper, nearly sotto voce, “Well, at least Mattis won’t let things get too crazy.” “At least Mattis knows what he’s doing.” Mattis was utterly real in an administration of phony tough guys, faux patriots, fantasy-based economic trade-war fetishists, and Trump’s broad array of lying shitbirds.

He was all substance and no flash. He was Mad Dog, the warrior monk, deeply read and supremely tough, and a man so clearly imbued with the core values that have made our military both fearsome and deeply respected at home and abroad. Unlike Trump’s low-rent “but muh troops” rah-rah, Jim Mattis truly loves the men and women in the armed services. He understands what orders to send American men and women into harm’s way imply. He knows how to precisely apply the war-fighting discipline and strategic vision that had made him one of the eminent military leaders of our generation.

Many members who serve on the foreign policy, defense, and intelligence committees still kept a channel open to the Mattis Pentagon; it was an island of stability and staff quality. Mattis resisted staffing the DOD with the usual Trumpian flotsam of used-car salesmen, mouth-breathing racist trash, hustlers, grifters, serial liars, hobo-organ harvesters, and alt-right kooks. Mattis ran a normal Republican DOD as hermetically as he could.

Just on the edge of Trump’s constant bleating about “his generals” was the sour odor of jealousy. It’s not hard to understand why.

Low, weak men like Donald Trump may pretend to praise people like Mattis, but always secretly revile those who possess virtues and values they lack. Trump resented Mattis for his accomplishments, his judgment, and his knowledge. Donald Trump, a man of the most shallow intellect and indifferent ability, faced a man who has forgotten more about war, diplomacy, and strategy that Trump has ever learned.

Mattis raised young Marines from every ethnic background into warriors fighting for a bigger idea than race or ethnicity; Trump is the most overt racist to hold the American presidency since Woodrow Wilson. Trump believes the troops exist for performance-art-like border-wall creation and parades to honor the Maximum Donald; Mattis knows they’re putting their lives on the line for the nation and the Constitution, and he honors them with missions that make America safer, not his ego bigger.

Trump knows on some deep, basal level that he’s a figure of mockery and cordial (at best) dislike by leaders of America’s traditional allies, and is seen as an easy mark by our adversaries. Trump saw how often Mattis had to clean up messes President Best Brain made in China, North Korea, Syria, Afghanistan, Iraq, and across Europe. Worse, he saw that the leaders of those nations respected Mattis in a way he couldn’t beg, borrow, or steal.

One supreme irony of Jim Mattis working for Donald Trump was apparent to me from the beginning.  Mattis wasn’t just a better man on every axis; Trump was the kind of man Jim Mattis spent his career training to defeat; the authoritarians and oppressors of this world, the big-bore despots and the small-bore warlords. The type of people Trump either admires or lets himself be manipulated by—Putin, Erdogan, Duterte, Kim Jong Un, and others—are the kind of men Mattis sees as obvious adversaries of the United States. Mattis sees the risks of failed states, while Trump seems determined to create one. Mattis understands American institutions; Trump monomaniacally craves royalty, a literal Imperial Presidency.

Mattis was and is a man of honor who did his best to steer Donald Trump away from disaster, and found himself hated for it. Mattis understood the importance and power of the U.S. military as an institution under civilian control, and as a repository of core American values. It must have been galling to him to serve this cowardly, venal, weak, and capricious man, but it was one more mission in a lifetime of service.

The departure of Jim Mattis from his role as secretary of defense is one more dangerous moment in a constellation of dangerous moments for this country, and this presidency. If you’re not nervous yet, you’re not paying attention.