Five years ago, the United States was completing its chaotic withdrawal from Afghanistan when the terrorist group known as the Islamic State Khorasan Province carried out one last murderous strike. An Afghanistan ruled by the Taliban, American policy makers feared, would become a haven for terrorists, as it was before the U.S. invasion in 2001. The Taliban is reportedly reluctant to allow al-Adel into Afghanistan, an apparent recognition that providing too much support to al-Qaeda could jeopardize its own interests.