It is hardly the first time that the United States has betrayed the Kurds, but President Donald Trump’s announcement on Sunday—that he’s pulling U.S. troops out of northern Syria and allowing the Turkish army to mow the Kurds down—is particularly shocking (even the Turks were surprised) and harmful to U.S. security too.

The likely consequences of Trump’s actions are not some unforeseen side effect; he acknowledged, and even welcomed, them explicitly. A statement released by the White House noted that Trump spoke with Turkish President Recep Tayyip Erdogan by phone. It then went on:

Turkey will soon be moving forward with its long-planned operation into Northern Syria. The United States Armed Forces will not support or be involved in the operation, and United States forces, having defeated the ISIS territorial “Caliphate,” will no longer in the immediate area.

In other words, Trump was telling Erdogan: Come on in. You’ll have an open field for killing.

For several years now, through the Obama and Trump administrations, Washington has relied on the Syrian Kurdish militia as the most potent fighters against ISIS, also known as the Islamic State. About 11,000 Kurds died in that fight. Now that they’ve played the lead role in ousting ISIS from its territory, Trump is abandoning them.

Removing the small contingent of U.S. troops could spring free thousands of ISIS fighters to resume their mayhem.

Trump tweeted Monday morning, “It is time for us to get out of these ridiculous Endless Wars, many of them tribal, and bring our soldiers home. WE WILL FIGHT WHERE IT IS TO OUR BENEFIT, AND ONLY FIGHT TO WIN.”

The statement fits his “America First” sentiment, but it’s misplaced here. The United States has only 2,000 troops throughout Syria, and until the withdrawal, only a few hundred of them were stationed at observation posts along the border. In the five years that they have been in Syria, only four Americans have been killed in the fighting. A quagmire this isn’t.

Given the relatively low cost, keeping the troops in place would very much be “to our benefit.” Among other things, the Kurds have been holding 59,000 suspected ISIS supporters in four detention camps. This has been possible only because U.S. troops have been guaranteeing their security. With those troops gone, the Kurds will have to focus on fending off the Turks.

In other words, removing the small contingent of U.S. troops—which has acted as a sort of safety cap—could spring free thousands of ISIS fighters to resume their mayhem.

This, too, is no unforeseen consequence; Trump recognizes it explicitly. The White House statement notes:

The United States Government has pressed France, Germany and other European nations, from which many captured ISIS fighters came, to take them back, but they did not want them and refused. The United States will not hold them for what could be many years and great cost to the United States taxpayer. Turkey will now be responsible for all ISIS fighters in the area captured over the past two years in the wake of the defeat of the territorial “Caliphate” by the United States.

It is risible that Erdogan has the ability or desire to assume this responsibility on Syrian soil. In fact, the Turks will more likely take the opportunity to send tens of thousands of Syrian refugees in Turkey back to their homeland, thus exacerbating the area’s instability.

The Turks have long viewed the Syrian Democratic Forces—the name of the militia that the Syrian Kurds have been leading—as a threat. They are closely tied to the Kurdistan Workers’ Party, a militant group within Turkey that has waged an insurgency against the Ankara government. Erodgan’s fear is that the two groups, together, could wage a serious battle against the Turkish state.

This situation has long posed complex challenges to Washington. The Syrian Kurds have been invaluable allies in the fight against ISIS. At the same time, Turkey is a member of NATO and hosts a U.S. air base where a few dozen nuclear weapons have long been stored. (An American security team has attested that the nukes are safe, but it’s crazy that they’ve been kept there through the tensions of the past few years or, for that matter, since the Cold War ended nearly 30 years ago.)

It is also true (and here Trump’s frustration with “endless wars” is understandable) that Syria is a bloody jumble of overlapping wars—sectarian, civil, regional, big-power proxy—over which the United States has little influence. It’s tempting to get out before we get sucked into a larger conflict. Everyone understands that the United States will get out at some point, and we should get out, but in the meantime, the troops are exerting a stabilizing influence—isolating ISIS, checking Iran, containing Russia, and, above all, supporting the Kurds, who are not only the best fighters in the region but also the most Western-leaning and democratic. It would be good to hammer down some diplomatic arrangements, to protect these goals and those people, before heading toward the exit.

But Trump has done none of this. He’s frustrated, he doesn’t like foreign interventions to begin with, he has no talent for diplomacy (and, after mass firings and departures, hardly any senior diplomats with any knowledge of the region), so he’s leaving—a decision he made without consulting his advisers, who, whenever he’s mulled going this route in the past, have opposed the notion unanimously.

Trump nearly took this step in December 2018. He was talking on the phone with Erdogan (just as he did on Sunday). Erdogan said that, with ISIS defeated, the United States had no reason to be in Syria. Trump agreed and said he’d pull out the troops right away. This was the move that finally pushed Jim Mattis to resign as secretary of defense (though, actually, he’d decided the previous summer to leave by the end of the year). Brett McGurk, the U.S. envoy to the region (a job he’d also held under Presidents George W. Bush and Barack Obama) soon followed. Eventually, Trump changed his mind. Now, 10 months later, with all the naysayers are gone, he changed his mind again.

Inside Syria, one of two things will happen as a result. Either the Kurds will be mowed down, or they’ll make an alliance with Syrian government, as they’ve already started to do, thereby strengthening Syrian President Bashar al-Assad. The violence will escalate. Probably Trump wouldn’t care either way, though the affected Syrian people will. In any case, the chances of a political settlement dim further—and the chances of an ISIS revival leap up.

Out in the rest of the world, this will be seen as another sign of Trump’s—and, therefore, America’s—erratic behavior and ultimate unreliability. Friends will seek alliances outside Washington’s orbit; foes will see an open path to pursue their interests with little fear of obstruction.

Some might say that Trump has proved once again that America First means America Alone. But in this case, he is not even putting America first; he’s violating all but the narrowest definition of American interests. That is because, at bottom, Trump has no idea what American interests are.