Much will depend on whether the United States is prepared to extend its role past the defeat of the Islamic State in an effort to prevent jihadi resurgence. As the Islamic State’s predecessor, al Qaeda in Iraq, demonstrated so dramatically, radicals can rebound quickly if fundamental threats to stability are left unaddressed. Limiting that danger in Syria would require continued . engagement focused on averting escalation between Turkey and the YPG and on promoting sustainable governance in areas the latter liberates from the Islamic State. For its part, the YPG could improve its appeal as a partner in stabilization by implementing necessary changes to its governance model.