On Monday, Rex Tillerson, the departing Secretary of State, cut short a visit to Africa to fly back to Washington. Before he left, he remarked that the nerve-gas attack recently carried out on a former Russian spy in Salisbury, England, was a “really egregious act,” but he also said it wasn’t entirely clear who was responsible. Later on Monday, though, the State Department issued a statement in which Tillerson expressed his “full confidence” in the British government’s assessment that the Russian state was almost certainly the culprit. (In the House of Commons on Monday, Theresa May, the British Prime Minister, said it was “highly likely” that Russia was responsible.)

“There is never a justification for this type of attack—the attempted murder of a private citizen on the soil of a sovereign nation—and we are outraged that Russia appears to have again engaged in such behavior,” Tillerson’s statement said. “From Ukraine to Syria—and now the UK—Russia continues to be an irresponsible force of instability in the world, acting with open disregard for the sovereignty of other states and the life of their citizens. We agree that those responsible—both those who committed the crime and those who ordered it—must face appropriately serious consequences. We stand in solidarity with our Allies in the United Kingdom and will continue to coordinate closely our responses.”

This was arguably the strongest condemnation of Russian behavior that the Trump Administration has ever issued. And it turned out to be one of Tillerson’s final official acts as Secretary of State. At 8:44 A.M. on Tuesday, Donald Trump announced Tillerson’s firing on Twitter. “Mike Pompeo, Director of the CIA, will become our new Secretary of State,” Trump wrote. “He will do a fantastic job! Thank you to Rex Tillerson for his service! Gina Haspel will become the new Director of the CIA, and the first woman so chosen. Congratulations to all!”

Some of Trump’s aides immediately insisted to reporters that the President hadn’t dismissed Tillerson because of the Russia statement. Citing multiple White House officials, the Washington Post reported that the White House informed the Secretary of State on Friday that he was going to be ousted. Zeke Miller, of the Associated Press, subsequently filled out this narrative, reporting via Twitter, “WH official says chief of staff John Kelly called Tillerson Friday and again on Saturday. Both calls to Tillerson, the official says, warned that Trump was about to take imminent action if he did not step aside. When Tillerson didn’t act, Trump fired him.” In brief remarks to reporters, Trump said he had been thinking about replacing Tillerson for “a long time,” because “We were not thinking the same.” He also said Tillerson “will be much happier now.”

At least one of Tillerson’s aides pushed back against this White House narrative, however. Elise Labott, CNN’s global-affairs correspondent, reported that Tillerson only found out from Trump’s tweet that he was fired. Josh Lederman, of the A.P., reported, via Twitter, “We got off the plane with Tillerson less than four hours ago. There was zero indication on flight home that this was imminent.” The White House reacted quickly to this counter-narrative. By early afternoon, the White House had fired the aide, Steve Goldstein, who contradicted its version of what had happened.

If Tillerson did know that the President was about to can him, his statement on Russia was perhaps a final act of defiance. On Tuesday, the Russian government again denied responsibility for the attack in Salisbury and said it wouldn’t respond to British claims unless it was provided with samples of the nerve agent used. Trump also spoke with May, finally, and, after the call, the White House issued a statement saying he agreed with her “that the Government of the Russian Federation must provide unambiguous answers regarding how this chemical weapon, developed in Russia, came to be used in the United Kingdom.” However, the statement stopped short of saying Trump agreed with the British assessment that the Russian government was very likely responsible.

It is certainly true that Tillerson’s departure wasn’t entirely unexpected. Although he has avoided criticizing Trump publicly, behind the scenes the former ExxonMobil C.E.O. hasn’t hidden his contempt for the President. Last summer, after Trump gave a wacko speech to the Boy Scouts of America, an organization Tillerson used to lead, Tillerson reportedly came close to resigning. In October, NBC News reported that after a meeting at which Trump called for a tenfold increase in the U.S. nuclear arsenal, Tillerson referred to him as a “moron” in a conversation with other officials. One of the NBC reporters would clarify that Tillerson used the term “fucking moron.”

After those revelations, which Tillerson didn’t explicitly deny, there were frequent suggestions that Trump was considering replacing him with Pompeo, a former Republican congressman. Despite this acrimony, the fact remains that Trump announced Tillerson’s firing barely twelve hours after he had forcefully sided with the British government against the Kremlin. Either Trump decided that Tillerson’s show of defiance was the last straw, or he was oblivious (or indifferent) to the impression that firing him at this juncture would create.

To be sure, there were policy differences between Trump and Tillerson—many of them. In addition to the Iranian nuclear deal, where Tillerson was more supportive than the President, trade and North Korea come to mind immediately. Last week, Tillerson reportedly warned White House officials that Trump’s proposal to impose tariffs on steel and aluminum imports would endanger U.S. national security. On Thursday, just hours before Trump agreed to meet with the North Korean leader Kim Jong Un, Tillerson told the reporters travelling with him in Africa, “We’re a long way from negotiations.”

Maybe that’s why Trump decided to act now, although it wouldn’t explain why he waited five days and then made the announcement on Twitter. It’s also possible that another factor played into his timing. Early Tuesday morning, the Washington Post reported that Roger Stone, the Republican dirty trickster and longtime Trump adviser, told an associate in the spring of 2016 that “he had learned from WikiLeaks founder Julian Assange that his organization had obtained emails that would torment senior Democrats such as John Podesta, then campaign chairman for Democratic presidential candidate Hillary Clinton.” This conversation took place “before it was publicly known that hackers had obtained the emails of Podesta and of the Democratic National Committee,” the story also noted.

As Reince Priebus, the former White House chief of staff, told Fox News’s Laura Ingraham, Trump pays a great deal of attention to how the daily news narrative evolves. After the Post’s scoop appeared, other news organizations leapt on it, and Stone’s name trended on Twitter. In all likelihood, the Post’s story, with its implication of possible collusion, would have dominated the day in cable news. But once the news of Tillerson’s firing broke, it slipped down the home pages, and Stone dropped off the trending list.

Whatever really happened, the fact is that Tillerson is gone—the first Cabinet secretary ever to be fired by tweet. Given his effort to gut the State Department, and the departure of many senior diplomats with distinguished careers in the department, Tillerson’s fall likely won’t be lamented in Foggy Bottom, or in many other places. But in the unique and alarming context of this Presidency, he seemed like a stabilizing and independent-minded presence. At least, he wasn’t a Trump flunky or a Bannonite ethno-nationalist.

With Tillerson’s departure so closely following the resignation of Gary Cohn, the former Goldman Sachs executive who served as Trump’s senior economic adviser, the circle around the President is getting even tighter. Pompeo, Tillerson’s replacement, is a Trump loyalist who has tried to downplay Russian interference in the 2016 election. And so it goes on.

This post has been updated to include the details of President Trump’s call to British Prime Minister Theresa May. It has also been updated to more accurately describe the location of Tillerson’s overseas tour.