First, Pentagon officials said they could pull out the remaining 3,500 American troops, almost all deployed at Bagram Air Base, by July 4 — two months earlier than the Sept. 11 deadline Mr. Biden had set. The plan would mean closing the airfield that was the American military hub in Afghanistan, but Defense Department officials did not want a dwindling, vulnerable force and the risks of service members dying in a war declared lost.

Second, State Department officials said they would keep the American Embassy open, with more than 1,400 remaining Americans protected by 650 Marines and soldiers. An intelligence assessment presented at the meeting estimated that Afghan forces could hold off the Taliban for one to two years. There was brief talk of an emergency evacuation plan — helicopters would ferry Americans to the civilian airport in Kabul, the capital — but no one raised, let alone imagined, what the United States would do if the Taliban gained control of access to that airport, the only safe way in and out of the country once Bagram closed.

The plan was a good one, the group concluded.

Four months later, the plan is in shambles as Mr. Biden struggles to explain how a withdrawal most Americans supported went so badly wrong in its execution.