President Joe Biden pauses as he speaks about the bombings at the Kabul airport, in Washington. AP

"America is back," goes President Joe Biden's catchphrase, but his unapologetic exit from Afghanistan shows America won't be back to business as usual.

Besides natural disasters, the president has had to contend with a multitude of other challenges.

At least 50,000 Afghans are expected to be admitted into the United States following the fall of Kabul as part of an "enduring commitment" to help people who aided the American war effort and others who are particularly vulnerable under Taliban rule, the secretary of homeland security said Friday.

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He is searching for ways to rescue the 100-200 Americans stuck in Afghanistan after the longest war in US history ended a matter of days ago. He is also confronting the Delta variant of the coronavirus that has plunged the country into an autumn of uncertainty only months after he declared independence from the disease at a July 4 celebration on the White House lawn.

American soldiers in Afghanistan prepare to return home.

Beyond the trauma of the Kabul evacuation, Biden is pitching a much broader retreat: a halt to using vast military resources to impose order and US values around the planet.

"This decision about Afghanistan is not just about Afghanistan," Biden said in what many see as a historic speech on Tuesday. "It's about ending an era of major military operations to remake other countries."

"Human rights will be at the center of our foreign policy but the way to do that is not through endless military deployments," he said. "Our strategy has to change."

Benjamin Haddad, director of the Europe Center at the Atlantic Council and an expert on transatlantic relations, called the speech "one of the most eloquent repudiations of liberal internationalism by any US president in the last decades."

For those Americans fond of imagining their country to be a unique, invincible superpower — winner of the Cold War, then awesome military interventionist everywhere from Iraq to Africa ever since — this is a shock.

For most, though, polls show Biden's pivot is likely to be popular.