A Vacancy at the Top Threatens the Group’s Global Operations It is only February, and already, the Islamic State (also known as ISIS) has had a rough year. ISIS’s supporters quickly went from cheering on a large prison break in northeast Syria to learning, days later, that the group’s reclusive leader, Abu Ibrahim al-Hashimi al-Qurayshi, was killed in a daring U.S. special operations raid. Before Qurayshi’s death, there was growing concern that ISIS might be resurgent. Beyond the prison break in Syria, where ISIS fighters had managed to maintain control of the facility for several days despite a powerful military...