Mr. Biden knew the risks. He has often noted that he came to office with more foreign policy experience than any president in recent memory, arguably since Dwight D. Eisenhower. In meetings this spring about the coming U.S. withdrawal, Mr. Biden told aides that it was crucial they avoid the kind of scene that yielded the iconic photographs of Americans and Vietnamese scrambling up a ladder to a helicopter on a rooftop near the U.S. Embassy in Saigon when it was frantically evacuated in 1975, as the Vietcong swept into the city.

Yet having decided in April to set the Sept. 11 anniversary as the date for the final American withdrawal, he and his aides failed to get the interpreters and others who helped American forces out of the country fast enough, and they were mired in immigration paperwork. There was no reliable mechanism in place for contractors to keep the Afghan Air Force flying as Americans packed up. The plan Mr. Biden talked about in late June to create what he called an “over-the-horizon capability” to bolster the Afghan forces in case Kabul was threatened was only half-baked before those Afghan forces collapsed…

Even the most seasoned hands in the politics of South Asia, like Ryan Crocker, a retired career diplomat who served as an ambassador to Afghanistan under President Barack Obama and to Iraq under President George W. Bush, thought there was more time.

“A prolonged civil war is a more likely outcome, frankly,” he said seven days ago on ABC’s “This Week,” “than a swift Taliban takeover of the entire country.” But he went on to say that Mr. Biden had “now taken complete ownership of President Trump’s” commitments to exit the country. “He owns it,” Mr. Crocker said. “And I think it is already an indelible stain on his presidency.”