The tempting comparison between the withdrawals of US forces from Kabul in 2021 and Saigon in 1975 has offered diminishing returns over the past 12 days.

Whereas about 7,000 people were evacuated from Vietnam (5,500 Vietnamese civilians and about 1,500 Americans), more than 95,000 people have left Afghanistan in a historic airlift since 14 August, the day before the capital fell to the Taliban.

But nor did the departure from Saigon face suicide bombers. Thursday’s attack by Islamic State in Kabul, which killed at least 60 Afghan civilians and 13 American troops, disrupted the evacuation effort and turned a crisis into a catastrophe.

The darkest day of Joe Biden’s young presidency left him with no good options. He must now decide whether to shorten, maintain or extend his deadline of 31 August for the full withdrawal of US forces.

To cut and run now would leave, by most estimates, hundreds of US citizens and many thousands of Afghan allies stranded in hostile territory. But to stay longer would be to invite further deadly attacks by Islamic State’s local affiliate and, beyond Tuesday, the Taliban itself on huge crowds at the airport.

“Every day we’re on the ground is another day we know that Isis-K [Islamic State Khorasan] is seeking to target the airport and attack both US and allied forces and innocent civilians,” Biden warned on Tuesday.

Having already disappointed international allies who craved a post-Donald Trump restoration of American leadership, the president also finds himself in a changed political landscape at home. Conventional wisdom has held that relatively few Americans care about Afghanistan or other foreign policy matters compared with the coronavirus pandemic and “kitchen table” issues.

But now, after the deadliest day for US troops in Afghanistan in more than a decade, American body bags will be flying home, a wake-up call to the insular and apathetic. The nation is in more need than ever of Biden’s empathetic side, not the one recounted in Our Man, a biography of the diplomat Richard Holbrooke by George Packer.

In a private conversation in 2010 with Holbrooke, the book says, Biden argued that America does not have an obligation to Afghans who trusted: “Fuck that, we don’t have to worry about that. We did it in Vietnam, Nixon and Kissinger got away with it,” – a reference to President Richard Nixon and his secretary of state, Henry Kissinger.

This tragedy, however, will feed America’s bitter polarisation and heighten the political temperature. Some Republicans have already demanded that the president quit. Josh Hawley, a senator for Missouri, said: “This is the product of Joe Biden’s catastrophic failure of leadership. It is now painfully clear he has neither the will nor the capacity to lead. He must resign.”

In the longer term, Thursday’s atrocity offers a glimpse of the chaos to come in Afghanistan, and just how dismally efforts at nation building and importing western-style democracy have failed. If the group known as Islamic State Khorasan wanted to grab the world’s attention and underscore the limits of US power, it surely succeeded.

Islamic State Khorasan is a sworn enemy of the Taliban and even more ideologically extreme. Its ranks include members of the Taliban who resented their leaders’ peace talks with the US. Its intervention on Thursday suggests the potential for further terrorism even after the Americans have gone.

This comes on top of the Taliban’s own threats to human rights, particularly those of women and girls, the weakness of government institutions and an economy hurtling towards the edge of a cliff. “This is a full-fledged humanitarian crisis,” said Bob Menendez, chairman of the Senate foreign relations committee.

Along with Saigon parallels, it has also been widely observed with frustration in recent days that 20 years’ worth of American blood and treasure in Afghanistan failed to make a difference. On Thursday, as the Pandora’s box sprang open, it seemed possible that it did make a difference – for the worse.

Mehdi Hasan, a host on the MSNBC cable news network, tweeted: “We invaded Afghanistan to fight a terrorist group, Al Qaeda, that attacked us. As we leave, we’re attacked by another terrorist group, ISIS, worse than Al Qaeda, & which didn’t exist when we invaded. I’ve said it before: all the war on terror gave us was more war & more terror.”