Acting against the advice of his generals and overruling some of his top foreign policy advisers, Mr. Biden made the decision in April that he could not ask more American troops — or their families — to sacrifice themselves for a war that he no longer believed was in the best interests of the United States or its allies.
The president has said that he did not want to call the parents of another Marine, soldier or airman killed in action in Afghanistan.
But the rapid takeover of the country by the Taliban caught the administration off-guard and set in motion a chaotic evacuation in which 6,000 American troops attempted to secure the Kabul airport against the Taliban and terror groups. Earlier this week, Mr. Biden rejected calls from lawmakers, activists and other world leaders to extend the American presence at the airport past Aug. 31, citing the potential for terrorist attacks.
Last Friday, as he pledged to evacuate all Americans and Afghan allies who wanted to leave the country, Mr. Biden vowed that “any attack on our forces or disruption of our operations at the airport will be met with a swift and forceful response.”
It was unclear on Thursday whether a military response of any kind was already in the works, or whether the U.S. troops on the ground had the capacity to strike back while also securing the airport.
But Gen. Kenneth F. McKenzie Jr., the head of the United States Central Command, said the military would pursue those responsible for the attack. And Mr. Biden later suggested that he would not let the attack pass without a response.