In a single cryptic tweet Wednesday, Donald Trump declared that the U.S. mission in Syria had been accomplished. “We have defeated ISIS in Syria, my only reason for being there during the Trump Presidency,” the president wrote. Shortly afterward, White House spokeswoman Sarah Huckabee Sanders confirmed that troops would begin returning home “as we transition to the next phase of this campaign.” It was not immediately clear what Trump or Sanders meant, or what would happen to the reported 2,000 troops currently working alongside Kurdish fighters against Islamic militants in northeastern Syria. The State Department abruptly canceled its scheduled press briefing. Defense Secretary James Mattis, confronted by reporters at the Pentagon, said he would not be making any comments. Foreign-policy experts were similarly dumbfounded.

Had Trump simply tired of his predecessors’ long-standing commitments in the Middle East, a geopolitical sinkhole for American blood and treasure? Did he knuckle under Vladimir Putin, who seeks to run Syria as a client state? Did he cave in to Recep Tayyip Erdoğan, who has railed against America’s partnership with Syrian Kurds, in order to secure Turkey’s cooperation in a regional pact with the Saudis? One former administration official offered a simpler explanation, citing Trump’s “isolationist views and a lack of interest in geopolitics.” Trump, this person explained, “doesn’t see the value for the U.S. in spending resources there.”

The one thing everyone seems to agree upon is that ISIS is not defeated, despite what the president says. Earlier this month, Joseph Dunford, the chairman of the Joint Chiefs of Staff, said the Islamic State remains a potent threat and that the U.S. has “a long way to go” in Syria. Last week, Brett McGurk, the special envoy for Syria, told reporters that “we just can’t pick up and leave,” and that doing so would be “reckless.” Just four days ago, the Pentagon said in a statement that the “mission in northeast Syria remains unchanged.” Any reports to the contrary, task force officials said, were just fake news “designed to sow confusion and chaos.”

Any explanation for the abrupt reversal in U.S. policy must begin by differentiating between Donald Trump and the administration he leads. According to The New York Times, Mattis and other high-ranking national security officials had tried repeatedly over the past several days to dissuade Trump from a full troop withdrawal, and were continuing to do so as recently as Wednesday morning. Trump, according to officials that spoke with the Times, pushed for a full withdrawal as soon as possible.

Several administration officials were reportedly blindsided. John Bolton, Trump’s national security adviser, had announced in September that the U.S. would not be ending its engagement until Iran’s presence in the region was stamped out. But Trump, who has frequently been at odds with Washington’s interventionists, disagreed. Back in April, Trump had unsuccessfully fought for a withdrawal from Syria within five to six months, surprising and confusing the foreign-policy establishment, but ultimately backed down after consultation with his advisers. On Wednesday, however, in a sign of his growing independence from the Pentagon, Trump pulled the plug all on his own. “The president said ‘Everybody out,’” a senior administration official told the Daily Beast.

Ever since Donald Trump’s stepped into the White House, the foreign-policy establishment has struggled to define the Trump Doctrine. On a number of issues, it has seemed that Trump’s guiding principle, when there is one at all, has been a desire to trample the legacy of Barack Obama. (Look no further than Trump’s decisions to withdraw from the Paris climate agreement, the Iran nuclear deal or the Trans-Pacific Partnership as examples.) In the case of Syria, however, Trump has rarely seemed guided by any psychological motivation or strategic logic at all.