Here’s how we get there: Current assurances of American support encourage Riyadh to be aggressive in its dealings with Tehran, rejecting options to de-escalate and seek a peaceful, diplomatic resolution (or at least a stalemate or balance of power both can accept). With the most powerful military in the world at its side, Saudi Arabia may well be emboldened to ratchet up hostilities toward Iran — while Iran, feeling threatened by its enemy’s position of strength, will become even more provocative in an attempt to prove itself a formidable adversary. For both sides, U.S. intervention fosters behavior that makes war more likely.

If mutual escalation continues, however, Washington eventually will have to choose: Do we follow through on the pledge to fight for Saudi Arabia, becoming embroiled in a major new conflict? Or do we disentangle from the region’s squabbles, declining to wage war at Saudi behest after years of suggesting we would do exactly that? Neither option is good, but both can be avoided by changing course now.

Saudi Arabia is unworthy of unconditional U.S. support. Like the Kurds, it is not a treaty ally of the United States — nor should it be, as its government is a brutal dictatorship well known to contribute to regional chaos, most visibly at present through its U.S.-enabled war in Yemen. Unlike the Kurds, it is a wealthy state perfectly capable of handling its own defense. Rather than deploying more American forces to protect an oppressive regime that has no obligation to do the same for us, Trump should finally make good on his many promises to bring U.S. soldiers home.