The group’s future may depend in part on who is actually leading the organization, said Blazakis, now a professor at Middlebury Institute of International Studies at Monterey. Baghdadi’s successor, identified by the ISIS media arm as Abu Ibrahim al-Hashimi al-Quraishi, may be the wanted terrorist also known as Hajji Abdallah, Blazakis said—a man with a $5 million reward on his head who was part of al-Qaeda in Iraq and may have even met Baghdadi as a prisoner of U.S. forces in Iraq. He is a religious scholar with operational experience—somebody, in Blazakis’s words, “who has showed that he can stay alive for a long time.”

Such a leader could help reconstitute the organization into a perhaps diminished version of its former self, both in its core territories and in commanding loyalty across 20-odd affiliated groups, each with membership ranging from a handful of people to thousands, as Travers said in his testimony. Finally, loyalists or returned foreign fighters in Western countries could carry out attacks. The United States, which supplied a smaller number of ISIS recruits than many European countries, would be more likely to face internet-inspired attacks, as it has in previous years, as opposed to the plots that plagued Europe, like those in Paris and Brussels.

Yet ISIS’s territorial decline has at least had meaningful short-term effects abroad. As Travers noted, both Europe and the United States have seen a marked decline in ISIS-inspired attacks in recent years—a fact he attributed to the gradual loss of the so-called caliphate. So far, Kurdish-led forces are still keeping thousands of suspected ISIS fighters off the battlefield.