But by early October, Obama was dropping more bombs on Syria than on Iraq. What happened? Kobani. ISIS launched an assault against this town on the Turkish border. Intelligence indicated the town would soon fall. Local Kurds were running out of ammunition. Turkish President Recep Erdogan lined up tanks, but refused to roll them forward; he also blocked Turkish Kurds from crossing the border to help their Syrian brethren. So, to prevent a humanitarian catastrophe, Obama sent in the drones and the fighter planes.

For a short while, the bombing forced ISIS militias to lay low and fall back. But then, like most resourceful armies (and it turns out ISIS is resourceful), they adapted to the patterns of airstrikes and kept fighting. To bolster their ranks, thousands of jihadists flocked to Kobani from all over, to help the holy cause and to fight the American devils, even if it meant dying in the process. (In fact, for some, martyrdom was part of the appeal.)

Suddenly, the fight for this little-known town took on vast symbolic significance. And if ISIS was telling the world that Kobani was a decisive battle along the path to the Islamic State’s victory, then Obama—who’d put American resources and credibility on the line—had little choice but to treat it as a decisive battle as well. If ISIS won, the propaganda windfall would be immense.