Noting that the United States is fighting at least eight distinct terrorist and militant groups under the AUMF, Preston suggested that there may never be an end to the war with America’s terrorist and militant enemies, at least in the traditional sense. “Indeed, in an armed conflict between a state and a terrorist organization like al Qaeda or [ISIS], it is highly unlikely that there will ever be an agreement to end the conflict. Unlike at the close of the World Wars, there will not be any instruments of surrender or peace treaties,” he said.

But there can be closure. And, in the recent past, Obama seemed to offer it. Speaking to U.S. troops at a base in New Jersey last December, the president said, “This month, after more than 13 years, our combat mission in Afghanistan will be over. This month, America’s war in Afghanistan will come to a responsible end.”

But Preston seemed to argue that this isn’t so, raising questions about what legal significance the president’s own statements have. U.S. military operations in Afghanistan “remain substantial,” he said. “Taliban members continue to actively and directly threaten U.S. and coalition forces in Afghanistan, provide direct support to al-Qa’ida,” Preston said, “and pose a strategic threat to the Afghan National Security Forces,” which U.S. troops are now training. “In short, the enemy has not relented, and significant armed violence continues.”