Americans mark the 20th anniversary of 9/11 on Saturday with troops finally gone from Afghanistan, but national discord -- and for President Joe Biden, political peril -- are overshadowing any sense of closure.

A whole generation has grown up since the morning of September 11, 2001.

9/11 attacks
Twenty years have passed since the 9/11 attacks by Al-Qaeda in the United States, but the fallout remains painful for Americans Photo: AFP / SETH MCALLISTER

In the interim, Al-Qaeda founder Osama bin Laden has been hunted down and killed. A towering new skyscraper has risen over Manhattan, replacing the Twin Towers. And less than two weeks ago, the last US soldiers flew from Kabul airport, ending the so-called "forever war."

Yet 9/11 never fully went away.

Joe Biden
US President Joe Biden wants to reunite a divided country Photo: AFP / MANDEL NGAN

The Taliban who once sheltered bin Laden are back ruling Afghanistan. The mighty US military has been humiliated. In Guantanamo Bay, accused 9/11 mastermind Khalid Sheikh Mohammed and four other men continue to await trial, nine years after charges were filed.

Even the full story of how the attack came to happen remains secret. Only last week did Biden order the release of classified documents from the FBI investigation over the next six months.

US Soldiers
US soldiers stand guard in the last days of the frantic evacuation from Kabul Photo: AFP / Wakil KOHSAR

Monica Iken-Murphy, who lost her 37-year-old husband Michael Iken in the World Trade Center, says this will be a "heightened" anniversary for many Americans.

But for her, as for many other survivors, the pain has never wavered.

"I feel like it just happened," she told AFP.

Tribute in light
The 'Tribute in Light' public art installation commemorates the 9/11 2001 terrorist attacks that destroyed the Twin Towers Photo: AFP / Ed JONES

Same as every year, simple, heart-wrenching ceremonies will unfold at each of the three places where Al-Qaeda hijackers crashed packed airliners, striking the cultural, financial and political hearts of the United States.

9/11 attacks
This file photo taken on September 11, 2001, shows Edward Fine covering his mouth as he walks through dust and debris following the collapse of one of the twin towers of the World Trade Center Photo: AFP / STAN HONDA

Ground Zero in New York was where the majority of the approximately 3,000 fatalities, including people from all over the world, were killed in the initial explosions, jumped to their deaths, or simply vanished in the inferno of the collapsing towers.

At the Pentagon, an airliner tore a fiery hole in the side of the superpower's military nerve center.

Joe Biden
US President Joe Biden attended the repatriation of the last service members killed in Afghanistan Photo: AFP / SAUL LOEB

And in Shanksville, Pennsylvania, the third wave of hijackers crashed into a field after passengers fought back, sending United 93 down before reaching its intended target -- likely the US Capitol building in Washington, a short flight further on.

Biden and First Lady Jill Biden will stop at each of these places on Saturday to "honor and memorialize the lives lost," the White House said.

Biden planned for this to be a pivotal day in his nearly eight-month-old presidency.

Taking over from Donald Trump in January, with the country still reeling from a Trump mob's assault on Congress, he promised Americans unity; exiting Afghanistan against the background of the 9/11 anniversary was going to be a big part of that.

Where Trump had promised the Taliban a deadline of May 1 for US troops to leave, Biden changed the pullout date to September 11 itself.

Even if he backtracked to a less politically sensitive cut-off of August 31, he clearly meant to own both the withdrawal and the anniversary.

However, instead of presiding over a moment of unity, Biden will traverse a country angry about the chaotic Kabul evacuation and stung by the broader realization of failure and defeat.

Even Biden's famed ability to show empathy, acting as consoler in chief, appears to be misfiring in the wake of the Afghanistan exit.

At a ceremony for the return to US soil of 13 US service members killed by a suicide bomber in Kabul -- the last Americans to die in the war -- Biden faced several furious grieving parents.

The angry father of one Marine told reporters later that he confronted the president over his son's death and that the encounter "didn't go well."

The mother of another of the dead service members posted on Facebook that Biden only wanted to talk about his "own sob story" and that she castigated him, saying her son's "blood was on your hands." She later invited Trump to the funeral.

When Biden tours the three sites Saturday, the weight of 20 years of history -- and the need somehow to turn the page -- will be on his shoulders.

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