Geopolitics is a contest of bad ideas, with winning defined as implementing the least-bad ones. Letting Turkey take control of Kurdish territory falls somewhere between “very bad” and “extremely bad” in this range; the only question is whether the alternatives fell into the rarely visited “shockingly, horrendously bad” portion of the spectrum. To leave the Kurds to Turkey amounts, first of all, to the total betrayal of an American ally, a group whose members have died in the desert by the thousands, so that we Americans didn’t have to revisit our bad dreams of the Iraq War by fighting in large numbers. The Kurds had their own reasons to despise the Islamic State—their ideology is Marxist and atheist, and ISIS would have slaughtered them all—but anyone who prefers Arlington National Cemetery to remain uncrowded owes thanks to the Kurds who died in our soldiers’ place. Letting our allies get annihilated is a fast way to ensure that we never have allies again.

Trump’s advisers (but who can advise Yahweh?) seem to understand this: His Defense Secretary James Mattis resigned in part because he refused to sell American allies downriver; and Eliphaz the Temanite, I mean Senator Lindsey Graham, spoke up this morning to say that if Turkey attacks the Kurds, he will try to sanction it and get it suspended from NATO. The advice seems to have elicited Trump’s threat to “obliterate” Turkey’s economy, and the mysterious, false claim that he had done so before. The complication here, however, is that Trump has saved an American ally (the Kurds) by pledging to devastate, according to his awesome whimsy, another American ally. It may seem odd to refer to Turkey—an autocracy with a theocratic touch—as an ally, but it is literally an ally, in the formal sense that it belongs to NATO, and is therefore in a very elite club, with obligations of mutual defense and neoliberal omertà that the Kurds lack. It is neither simple nor wise to treat that relationship recklessly.

Read: The Kurds: Betrayed again by Washington

Nor is it possible to implement a foreign policy in Syria without some Turkish cooperation. Recall that when the Islamic State seized Mosul, Turkey had to negotiate for the lives of the dozens of Turkish diplomats kidnapped from its consulate. The terms of that negotiation remain unknown, but we do know that in the next year or so, Turkey and the Islamic State somehow avoided major confrontation, almost as if they had a time-limited armistice. During that time the fight against the Islamic State stalled.

Allies and potential allies will watch this farce of geopolitics and again wonder what an alliance with America is really worth, if it can be flushed away one night and restored the next—or if there’s always the part where Trump says something, then the part where he takes it back. Trump’s signature trait as a real-estate mogul was that a Trump deal was never, ever a deal. His word meant nothing, and if you thought it did, he’d snatch up your money and walk away with it. As president he is no different, and by this afternoon there is not one ally but two who have been reminded never to trust him—to extend him no credit, to assume he’ll reserve the right to rewrite, unilaterally, the terms of your agreement, and force you to accept his new terms. The old diplomatic wisdom was that you should reward your friends and punish your enemies. To act completely undependable, both as an enemy and as an ally, serves no obvious purpose.