“Everybody’s worried about a repeat of the Saigon images,” said Brian Katulis, a foreign policy expert at the liberal Center for American Progress, referring to the chaotic April 1975 evacuation of the American Embassy in South Vietnam’s capital. Desperate Vietnamese clung to the struts of departing helicopters as the city was being conquered by Communist forces.

Americans remain focused on domestic matters like the coronavirus and the economy, and are unlikely to care much that the Taliban have captured unfamiliar cities like Kunduz, said Mr. Katulis, who has studied public opinion about foreign policy.

“But this could change,” he added. “If you have a parade of horribles continue to unfold in Afghanistan, it could seep into the public consciousness the way Iraq did in 2013 and 2014” when the Islamic State stormed across that country after American troops withdrew.