Al Qaeda’s numbers in Afghanistan have slightly increased, from four hundred fighters before 9/11 to around six hundred before the Taliban takeover, experts say. U.S. and Afghan operations eliminated senior leaders and largely shut down the training camps that once operated in the country, but the movement has adapted. In October, the Afghan military claimed that it had killed the red-bearded Egyptian Husam Abd al-Rauf, whose nom de guerre was Abu Muhsin al-Masri. He was on the F.B.I.’s “Most Wanted Terrorists” list. Despite Al Qaeda’s low public visibility, however, experts said that the group was pivotal in the Taliban’s sweep across Afghanistan. It provided “the élite backbone” in the Taliban campaign, Hoffman told me. “In recent years, Al Qaeda has been the force multiplier behind the Taliban” by enhancing intelligence, communication, and fighting skills. Its fighters were “more cosmopolitan and better educated than the Taliban, who are coming down from the mountains. They bring a lot of skills to an army of country bumpkins,” he added. “The number was not large, but it was outsized in its significance.”

There was no secret about the ongoing Al Qaeda presence or its willingness to fight side by side with the Taliban, despite claims by successive U.S. Presidents. In December, the Afghan defense ministry announced that it had killed fifteen Al Qaeda operatives fighting with the Taliban in southern Helmand Province. In recent weeks, the numbers of Al Qaeda and isis-Khorasan, the franchise in Afghanistan, both grew after the Taliban released some five thousand prisoners from Pul-i-Charkhi Prison at the Bagram Airfield on August 15th. The U.S. abruptly abandoned Bagram, its largest military base of operations, last month. The doors to other prisons were unlocked as the Taliban swept across the country. On Saturday, the U.S. Embassy—which is now working out of the Kabul airport—warned Americans still in Afghanistan not to go to the airport unless provided specific instructions, because of a new threat from isis. The Afghan wing of the Islamic State is a rival of both the Taliban and Al Qaeda, and an enemy of the United States. U.S. officials have been worried that isis might try to ignite a confrontation at the airport, where Taliban and U.S. forces are only a few feet apart.