That, however, left unanswered the question of what it would mean if Afghanistan was no longer an active zone of armed conflict, even as fighting raged elsewhere thousands of miles away.
Mr. Haroon’s case may be stronger since he is an Afghan citizen, as opposed to other detainees who the government says traveled to Afghanistan to join Osama bin Laden’s Islamist movement. There is only one other Afghan still at Guantánamo, Muhammad Rahim, 55, but he presents a more complex case.
He was initially held in C.I.A. custody as a “high-value detainee,” and his 2016 intelligence profile describes him as a courier and facilitator for Al Qaeda — including for Bin Laden — who had advance knowledge of the Sept. 11 attacks. He has never been charged with war crimes.
If the evidence is strong that Mr. Rahim worked directly for Al Qaeda, the government can argue that wartime authority continues to exist to hold him to prevent him from returning to the fight, even if the warfare involving the United States in Afghanistan is over. But his lawyer, Cathi Shusky, a federal defender in Ohio, argued that the evidence was weak.
“There’s a reasonable explanation he wasn’t part of either” Al Qaeda or the Taliban, said Ms. Shusky, who said many of the details of his case were classified, preventing her from elaborating. “There is some twisting of the narrative. I think when the facts are fully revealed, it will show his continued detention is not lawful.”
A U.S. military representative for Mr. Rahim, told an administrative review board in March 2016 that Mr. Rahim regretted his past and wanted to return to his two wives and seven children in Afghanistan. His motivations were not ideological, the representative said, rather “he only did what he did for money, so he could feed his family.”
His federal court petition for release has been on hold for years while he sought release through the board, which has repeatedly declared his detention a national security necessity. But Ms. Shusky said she and another lawyer were planning to revive his habeas corpus case in light of the decision to pull out of Afghanistan.