Aaron Y. Zelin writes: Al-Qaeda is having a difficult time, given ISIS battlefield gains in both Syria and Iraq. Continued success for ISIS, of course, is by no means guaranteed, especially given the group’s tendency to overplay its hand with locals. But unlike in Iraq a decade ago, there is no force like the United States on the ground to consolidate insurgent gains against ISIS. As seen in Syria since January, many nationalists, mainstream Islamists, and even JN [Jabhat al-Nusra] have been unable to strategically defeat ISIS. And now that ISIS has gained new resources in the recent Iraq battles, it is pouring them into new offenses and regaining lost territory. Further, the reality of a proto-state and ISIS’s willingness to try to govern — this khilafa project, as many within the group call it — is quite appealing to jihadists. ISIS is not only talking the talk about establishing an Islamic state, it is walking the walk. This has attracted many foreign fighters to its side.

In becoming the beacon for foreign fighters over the past year, ISIS now controls many recruitment and facilitation/logistics networks. Further, those who have fought with ISIS have made connections with one another and will likely keep in touch when they return to their places of origin. The solidarity and brotherhood established through fighting on the front lines and enduring the same hardships cements these relationships, which will be important for the future of the jihadist movement. Additionally, individuals like winners and, unlike al-Qaeda, which has not had a clear victory in a decade, ISIS continues to build its prestige and legitimacy within the overall movement.

The composition of foreign fighter flows to Syria (and now to Iraq again) indicates that the movement’s future is being decided by Saudis, Libyans, Tunisians, and Jordanians. In terms of the Saudis, one question to be answered is whether returnees to AQAP can flip or execute a coup against AQAP’s leadership. AQAP remains loyal to Zawahiri given its emir Nasir al-Wihayshi’s relations with bin Laden, which go back to Afghanistan. That said, if Wihayshi is killed in an American drone strike, anything could happen. AQAP, still viewed as al-Qaeda’s strongest branch, is a bellwether and if it leans toward ISIS in the near to medium future, ISIS will have won the war against al-Qaeda. Similarly, with ISIS’s victories next door in Iraq, members of JN may have more cause to defect back to ISIS, which could be a fatal blow to al-Qaeda as well.