The fall of ISIS's caliphate should have concluded the military mission in Syria and led to a withdrawal of all U.S. forces. Failure to do so encouraged the Kurds to seek autonomy rather than protection from Damascus, which would have kept Turkey out, ISIS down, and the Kurds reasonably safe. Staying entangled in Syria has precipitated a crisis between Turkey and the Kurds, and left the U.S. with no appealing options. While the U.S. and Kurdish forces forged a partnership of convenience and mutual benefit to defeat a common adversary, the U.S. did not agree to adopt other Kurdish interests, nor should it. An orderly withdrawal of all U.S. forces is the only way to promote a sustainable status quo.
When President Obama, without congressional authorization, ordered U.S. forces to intervene in Syria, the mission was clear: liberate ISIS-held territory. That mission has been achieved. Leaving behind U.S. forces in Syria involves large risks without any security upside: it threatens to drive adversaries into allying against the United States; to inflame Islamist-nationalist sentiments in Iraq and Syria, making U.S. forces targets; and to risk U.S. conflict with Russia, Iran, Turkey, and Syria for no good reason. Staying also ties down U.S. forces and limits their focus on core missions. With ISIS’s “caliphate” destroyed, U.S. troops have achieved all they reasonably can and should be fully withdrawn.