Last Tuesday, after waking up to tweet about the previous day’s F.B.I. raid on his lawyer’s office (“A TOTAL WITCH HUNT!!!”), President Trump called one of his outside Republican advisers to ask what to do about Syria, and its latest chemical-weapons attack on civilians. “We should bomb the shit out of them, Mr. President,” came the answer, which was exactly the one Trump seemed to be looking for. Over the weekend, the President, outraged by the photographs of dead children in the Syrian enclave of Douma he had apparently seen on TV, had tweeted vows of retaliation against “Animal Assad,” and the Syrian leader’s backers in Russia and Iran. Trump’s hawkish new national-security adviser, John Bolton, who had started work that Monday, was also pressing for punishing strikes. On the phone call, Trump listened approvingly to the hit-’em-hard advice: that, politically, “the minimum should be bigger than it was last year,” when Trump had launched a single-day strike on a Syrian airfield, designed—unsuccessfully, as it turned out—to deter future chemical-weapons use.

By Friday evening, when the American cruise missiles actually started flying, the vaunted attack had been reduced to a single predawn volley against three Syrian government chemical-weapons facilities, carefully chosen to avoid hitting known Russian or Iranian bases and thus escalating a war from which Trump himself had recently demanded an exit. The strike was bigger than last year’s, but hardly the sustained response with “all instruments of our national power” that the President promised in his televised address announcing the attack.

The reason, as it so often has been over the tumultuous first year and three months of the Trump Presidency, was Defense Secretary James Mattis.

Blunt and no-nonsense, a retired four-star Marine Corps general deemed so tough on Iran that President Barack Obama’s team often clashed with him, Mattis has turned into the secret “peacenik” of the Trump Administration, as a former government official put it to me last week. A year ago, Mattis had also been wary of the first Trump-authorized missile strike on Syria, at least in the absence of a broader strategy toward the civil-war-torn country that eludes the Administration still. In the year since then, there had been numerous other occasions—some reported, many more not—when a blustering Trump had demanded military action only to run up against the calm but implacable opposition of his defense chief. And that dynamic more or less played out again last week in the White House Situation Room. “He was inclined to a farther-reaching strike,” the Republican adviser who spoke with Trump said, “but he deferred to Secretary Mattis.”

The secretary may have prevailed this time, but, as reports of the internal debate surfaced, officials in Washington were left to wonder: At what cost? Foreign-policy veterans told me they were worried that Trump would finally tire of Mattis, as he has soured on so many other top advisers, though White House officials were at pains to deny any sense of a rift between the two. (“False,” the spokeswoman Sarah Huckabee Sanders said in an e-mail, when I asked about the Trump adviser’s sense that Trump had deferred to Mattis on the strike.)

Still, Syria is just one on a long list of issues, from Trump’s threat to withdraw from the Iran nuclear deal to his unilateral recognition of Jerusalem as Israel’s capital, from the U.S. exit from the global climate-change pact to the imposition of trade tariffs, on which Mattis has now been publicly identified as disagreeing with his loyalty-obsessed boss. “Either you conclude his influence is very high because of where Syria turned out,” one of the city’s national-security eminences, who has met with many of Trump’s officials in recent months, told me, “or it’s the beginning of the end.”

The April 13th Syria attack capped what was, even in this Trumpian era, a remarkable bloodletting on his national-security team. Exactly a month earlier, on March 13th, Trump had fired Secretary of State Rex Tillerson and promoted the C.I.A. director Mike Pompeo in his place, setting off a purge that continues four weeks later. Nine days after Tillerson was dumped by tweet, Tillerson’s bitter internal rival, the national-security adviser, H. R. McMaster, was also abruptly replaced. Bolton, such a contentious figure that the chief of staff, John Kelly, banned him from the Oval Office last summer, was hand-picked for the job by Trump himself in what everyone took, correctly, to be a rebuke to Kelly, who was now presumed to be next to go. When Bolton arrived at the White House last week to succeed McMaster, he immediately ousted the Homeland Security adviser, Thomas Bossert; both deputy national-security advisers; the National Security Council spokesman; and assorted other aides amid the Syria war meetings. More firings are expected. Meanwhile, both Kelly and the high-profile U.N. Ambassador Nikki Haley have been ensnared in the infighting, drawing fire from the President himself.

Mattis emerged from the dizzying month still seemingly intact, but he, too, has been diminished in ways that are not yet entirely clear: Will Pompeo prove to be an ally or a rival of the Defense Secretary? Will Bolton, having lost round one over Syria, be more successful against Mattis in future policy disputes? Will Trump, emboldened after firing Tillerson and McMaster, decide to jettison a Pentagon chief who is also often not on the same page? Worried Democrats and anti-Trump Republicans quickly christened the hawkish new team of Bolton and Pompeo a “war cabinet” and warned of a militaristic turn in Trump’s policy, but it’s already clear that they don’t have the actual warrior among them on board. “Mattis may indeed be the last man standing,” Julianne Smith, a former senior Pentagon official who later became Vice-President Joe Biden’s deputy national-security adviser, said, “but for how long?”

When they took office, Mattis, Tillerson and McMaster were portrayed in the press as an “axis of adults,” who, together with Kelly, the chief of staff, would serve as steady hands constraining a volatile, inexperienced President. Even now, after it has all played out, the myth persists. But that was not, in fact, the case, current and former White House, Pentagon, and State Department officials, as well as other advisers close to the protagonists, told me. McMaster had a falling out with Mattis and Tillerson that was more than just the standard political jockeying over power and access: theirs was a dispute at least in part about Trump himself, and over just how much to accommodate the demands of the capricious, often angry President they had signed up to serve. “It’s a bully’s approach to the world,” the former government official told me. The President would say, “This made me angry today. I want to punch them.’”

The factional warfare among the “axis of adults” regarding how to respond to Trump was pervasive. Should they give in to the President’s tantrums? Find a way to redirect him when he demands a plan to blow up Iranian fastboats in the Gulf? Or publicly discuss military options in Venezuela without warning? All of it, of course, was playing out against the backdrop of global events that wait for no office politics, from the escalating tensions with Russia to the drumbeat of the Syrian civil war.

On one side were Mattis, Tillerson, and Kelly, each of whom to varying degrees sought to push back against the President; on the other was McMaster, who made his natural allies furious for what they saw as his habit of trying to accommodate the President’s demands, even if they were far-fetched. “General McMaster was trying to find a way to try to execute, not to tell him no,” the former government official told me. “Every answer was a big military contingent.” For their part, McMaster’s allies largely blamed Tillerson and Mattis (the “Gang of Two,” he called them), insisting that, as one put it, “H. R. got caught in the middle. The President wants strategy; it’s hard to do it without a Secretary of State.”

How bad did it get? I heard stories of intrigue so rampant, they made me wonder how some of these officials ever had time to think about matters of state; some of it seems astonishingly petty, much of it remarkably self-defeating. Tillerson, for example, personally distrusted Heather Nauert, the former Fox News anchor the White House sent to be his spokeswoman, so much that he wouldn’t allow her to travel with him despite repeated entreaties; his close advisers believed she was informing on him back to the Trump loyalists out to get the secretary. (The White House seemed to confirm which side she was on when, within hours of Tillerson’s dumping, it fired the under-secretary nominally overseeing Nauert’s office and promoted her in his place. Nauert, Sanders told me in her e-mail, “is highly respected and liked in the White House.”)