President Donald Trump just reversed one of the biggest decisions of his presidency.

As recently as December, he had vowed to bring all 2,000 American troops home from Syria — he even tweeted a video of himself announcing the move. But months of backlash from lawmakers in both parties, military leadership, and European allies — plus the potential endangerment of a US-backed force in Syria — apparently led Trump to change his mind.

On Thursday, White House press secretary Sarah Sanders announced that the US would keep 200 troops in the country. Expanding on that during an appearance Friday on Fox & Friends, she said, “At the end of the day the president wants to bring our troops home and he is working towards that and he wants to do that in a safe and peaceful way, in the best way possible, to make sure we have complete safety for our troops abroad.”

But apparently that’s wrong. On Friday, it appeared that 400 troops — not 200 would stay in Syria after all.

After historic victories against ISIS, it’s time to bring our great young people home! pic.twitter.com/xoNjFzQFTp — Donald J. Trump (@realDonaldTrump) December 19, 2018

US troops are in Syria to help defeat ISIS, mostly by training the Kurdish-led Syrian Democratic Forces. However, Trump has long questioned American troops’ presence in the country. As far back as the presidential campaign, he made clear he was against America’s involvement in foreign wars, which in part led him to make his surprising announcement late last year.

But Trump’s decision underscored two major flaws in his withdrawal plan.

First, he said US troops could leave Syria because ISIS is defeated. He is somewhat right in that the terrorist group is mere days from losing all of its territory in Syria (and Iraq). The problem, though, is that both the Pentagon and the US intelligence community say ISIS still has thousands of fighters left in the area. If American troops were to withdraw now, then, there’s a good chance ISIS could recoup its major losses.

Second, America’s departure could prove deeply problematic for US allies in Syria. That’s because of Turkey, the NATO ally that is trying to eradicate the US-backed Kurdish fighters there. Ankara considers the Kurds near its border a serious terrorist threat, and plans to remove them by launching an all-out military assault. If US troops go, that makes a Turkish attack more likely.

Further complicating the matter is that both France and the UK said they would no longer keep their troops engaged in Syria if the US left. The new decision to keep at least 400 US troops there, though, might compel them to stay.

“The Europeans won’t deploy to or stay in Syria without some form of US presence,” Jennifer Cafarella, a Syria expert at the Institute of War in Washington, told me. “So I expect the intent is that these troops are the ‘anchor’ that enable the European presence, which would hopefully deter the Turks.”

It’s unclear what, exactly, the US troops will do, although it’s expected that some will stay in northern Syria to keep Turkey at bay and some in the south to spy on Iran’s support for Syrian President Bashar al-Assad.

What is clear, though, is that Trump’s plan for a full withdrawal is temporarily dead.