On Aug. 26, as the United States was rushing to evacuate Americans and their allies following the Taliban’s rapid advance across Afghanistan, a suicide bomber attacked the crowds surrounding Kabul’s airport, killing 13 U.S. service members and as many as 170 Afghans. It was the deadliest day for U.S. troops in Afghanistan since 2011. Within hours, the Islamic State-Khorasan claimed the attack, a sobering reminder that despite the Islamic State’s territorial defeat in Iraq and Syria two years ago, the group has not disappeared.