It was a beautiful morning. George W. Bush sat in that classroom with little children learning to read. He's had the news about the first plane whispered in his ear and there's confusion and fear and anger plastered all over his face. And humiliation. He doesn't know what's happening.
The camera rolls: you can see all this in the new documentary "9/11: Inside the President's War Room". Here's the president of the United States, in his first year on the job, trying to smile for the kids. No one comes to help him. He doesn't know what to do. It's a powerful metaphor.
Was 9/11 the moment when everything began to fall apart?
So many things we knew or were told we could rely on: they're gone now. The global stability that followed the fall of the Berlin Wall. The enduring reliability of American democracy. The inexorable rise of human rights and ever-increasing prosperity for all.
Also gone: the military assumption that might is right. The 200-year-old Enlightenment assumption that reason prevails. The Western assumption that we control our own destiny.
In 1992, the American political scientist Francis Fukuyama wrote a book called "The End of History and the Last Man". It created a storm.
Fukuyama didn't really think history had ended. He believed that after 2000 years and more, the engine for progress was no longer the great, bloody contest of world powers.
The Soviet Union had collapsed. Capitalism and democracy – especially of the American variety – had no serious foe. The world would henceforth move smoothly forwards: a succession of fine days, forever more.
Fukuyama did not anticipate that planes with hundreds of people on board would be turned into missiles to destroy buildings with thousands of people inside them.
Predictions are such folly. You put the washing out and that makes it rain. In 1899 the US Patent Office wondered if it should close, because it seemed like most things of value had already been invented. You declare the age of Pax Americana and boom, it's time for war.
The second plane flies out of the blue sky of that beautiful morning and into the building and changes your understanding of how the world works. The first building collapses and the world changes all over again. You know that everyone in that plane and those buildings has died, while you watch. A fine day, filled with dust and smoke and horror.
9/11 enlarged all the things about being human. Courage and compassion, the bonds of community and faith and love. The great desire to help. The skills we bring to crisis. Also, the aloneness and fear and sense of futility we cover up as best we can with all the stuff of our lives.
Also, the abiding sense of hope that somehow always claws its way to the surface. And with it, a sense of moral purpose, which is both the best and the worst thing of all. Everyone gets to their feet with a shining sword in their hand.
It took only a week for America to invade Afghanistan, in search of Osama bin Laden. By the end of the next year, Bush was at war with Iraq as well, an eager Tony Blair riding shotgun at his side.
They were told by their own military and intelligence experts that Iraq did not have weapons of mass destruction. They knew Iraq had played no role in the 9/11 attacks and did not even support al Qaeda. But they went to war anyway.
Perhaps the motive was simply opportunity. Led by Vice-President Dick Cheney, the neoconservatives in Bush's Cabinet saw their chance to realise a dream.
At its best, that dream was of a world where liberal democracy would triumph. At its worst, it was a fever dream of war, accepting whatever casualties might happen, as long as they happened on foreign soil, because that was the way to make money.
The deserts of Iraq and the mountains of Afghanistan were going to be neoconservatism's great proving grounds. Instead, they became the place where Fukuyama's grand conceit went to die.
It's hard to overstate the rottenness that set in. Racism swept the Western world, focused on everyone who looked like they might be Arab, therefore might be a terrorist, therefore probably was.
And in America, where the global financial crisis saw mortgage disclosures on 11 million homes and a 20-year drought was ravaging the land, people became profoundly disconnected from their civic institutions. Donald Trump was their avenging angel.
Neither war achieved its political goals. There was social progress: once women were not confined to their houses in Afghanistan, literacy rose and infant mortality fell by 50 per cent. But now what?
Hundreds of thousands of people died and millions became refugees. American ideals were debased beyond recognition in Abu Ghraib and Guantanamo and, often, in the valleys of Afghanistan.
It was as if, rather than history having ended, it was simply forgotten.
And as America already knew from Vietnam, wars of conquest don't liberate people, they breed resistance. The war in Iraq created Isis.
Bush and Barack Obama are both culpable. Bush for starting the war, Obama for ending it by backing an Iraqi leader who was violently suppressing democratic opponents. Al Qaeda in Iraq, which became Isis, became their champion.
New Zealand refused to accept a military role in Iraq, which was a remarkable achievement. In Afghanistan, our troops did much to help build civil society in Bamiyan Province.
But we were corrupted in that country anyway: the SAS delivered prisoners to their allies for torture and there were avoidable civilian deaths on their watch. They breached the Geneva Convention and the Defence Forces and Government both lied to us about it.
And as the longest war in modern times ended last month, we discovered there were no plans to evacuate most of the people who had helped our soldiers stay safe. It is a mark of shame.
When there's terrible oppression in the world, we want to help. Iraq and Afghanistan both demonstrated the folly of trying to do it through military conquest, but they also reminded us how much the UN lacks its own effective moral authority.
Twenty years and two wars after 9/11, we're still looking for better ways to make a better world.
Faith has changed. Islam teaches humility, compassion and service and yet terrible things are done by extremists in its name. Christianity is just the same.
Secular faith is also on the block. In his book "A Promised Land", Obama declares: "The world watches America – the only great power in history made up of people from every corner of the planet, comprising every race and faith and cultural practice – to see if our experiment in democracy can work".
It's a tremendous ideal and he's right, we are watching. Although perhaps with not quite as much hope as he imagines. Superpowers have always had more to learn than teach about human rights and democracy.
Since 9/11 so many people have forsaken that ideal. Al Qaeda and Isis have given licence to lone wolf "jihadists" and white supremacists believe their own brand of terror is licensed too. We've seen both these things here.
And yet we have learned the power of kindness. And we hold on to something we do not think can ever be extinguished: the hope that a fine day will be a good day.