The U.S. commitment to the Kurds was highly cost-effective and productive in fighting ISIS as part of a “by, with and through” approach to harnessing Kurdish strength on the ground. But even without America’s long history of making promises to the Kurds it could not keep, it should have been clear that after the physical dismantling of the ISIS Caliphate, the U.S. relationship with the SDF would become increasingly fraught. Indeed, Washington eventually would have been faced with the choice of supporting either a Kurdish/Arab militia tied however loosely to the PKK, a designated terror group perceived by Turkey as an existential threat, or Turkey, a NATO member.

The SDF did not sacrifice its fighters out of love for America; rather, it hoped to harness U.S. power to help protect Kurdish territory and guarantee autonomy in a future Syria. Washington and the Kurds formed a marriage of convenience to defeat ISIS, but over the longer term there would have been a reckoning over divergent goals. The territory the SDF controlled was roughly the size of West Virginia and it is sandwiched between a deeply suspicious Turkey and an Assad regime equally resolved to bring all of Syria under its control. Consequently, survival of the SDF would have depended on Washington’s willingness to help protect the Kurds from Turkey and likely a long-term U.S. presence and security guarantees as well as support for Syria’s stabilization and reconstruction. Perhaps a future U.S. administration would have accepted these responsibilities in order to contain ISIS and gain leverage over the Assad regime. But the Trump administration was not about to get drawn into the Syrian vortex. And it is an open question whether the administration that follows Trump (be it in 2020 or 2024), Congress and the American public would be prepared to foot the bill of not just fighting jihadists but getting drawn into what would have been a nation-building exercise as well.