In a nutshell: The Kurds, with U.S. encouragement and support, bravely beat down the Islamic State in northern Syria; they hold many Islamic State fighters and their families imprisoned in the region; U.S. officials trying to broker peace between the Kurds and neighboring Turkey recently convinced the Kurds to scale back some of their defenses along the Turkish border; and now that the Kurds’ defenses are down, the American president has told Turkey to go ahead and attack.