From a March 2021 Atlantic article by George Packer:
In a Senate speech on April 23, 1975 Joe Biden argued that the president lacked the authority to rescue any Vietnamese. “I do not believe the United States has an obligation, moral or otherwise, to evacuate foreign nationals” other than diplomats of third countries, Biden said. “The United States has no obligation to evacuate one, or 100,001, South Vietnamese.” The U.S. should leave the task of protecting them to “the organizations that are available” and “diplomatic channels,” he added. A week later, North Vietnamese tanks entered the grounds of the presidential palace in Saigon just hours after the last helicopter carried the last Americans out of Vietnam.
Seventeen thousand Afghans…. are waiting for the machinery of the U.S. government to decide their fate. The process is so byzantine and opaque that even American lawyers representing Afghan clients have a hard time navigating it. Applications for a Special Immigrant Visa, or SIV—including proof of U.S. employment, a letter of recommendation from a U.S. supervisor who might have left Afghanistan years before, employee badges, and a statement of threats—go first to a building in Portsmouth, New Hampshire, that houses the National Visa Center. There they disappear into a bureaucratic black hole, often for two or three years at a time. The SIV section is staffed by only a handful of people, mostly contractors.