Just a month ago, as President Biden defended his decision to end American involvement in Afghanistan, he said a Taliban takeover was not inevitable.

“Do I trust the Taliban? No,” Mr. Biden said. “But I trust the capacity of the Afghan military, who is better trained, better equipped and more competent in terms of conducting war.”

But in the last seven days, the single most stunning week in two decades of war, that military collapsed. Vital cities fell to the Taliban one after another. A sense of panic has taken hold.