Two years ago today, out of a clear blue sky, 19 determined men exposed the vulnerability of the most powerful nation the world has ever known. The reverberations of that attack on 9/11 will echo globally for at least a generation.
Already two wars have been fought - at no small human and economic cost - and the shape of the Middle East is being recast. World politics, international alliances, and institutions, have been shaken or are being refashioned. Not least this is because a traumatised American public, once reluctant to countenance body bags returning from military adventures, has been persuaded, for the time being, that a US role as an international policeman is justified. And a price may have to be paid.
Painful as it was to the American people, however, the 9/11 strike - ostensibly against America's ability to project its power across the world - must rank, in the medium term, as a most spectacular own goal. Not only did al Qaeda lose its safe haven in Afghanistan and a large part of both its leadership and rank-and-file, but its actions provided the political opportunity long sought by the most hawkish of America's leaders to accelerate the rearming of the country and to complete unfinished business in Iraq. Any weighing, two years on, of the relative balance of world forces can come to no other conclusion but that the US imperial project, whatever that may be, has been strengthened.
Yet Osama bin Laden was never interested in the short to medium term. His battalions were never any match, head to head, for the might of the US. His was, and presumably still remains, the long view. By provocation and by "spectaculars", what the old Russian revolutionaries called the "propaganda of the deed", he sought both to rally the alienated of the Muslim world to his banner and to provoke the US into an overreaction that would expose its ostensibly evil purposes yet more clearly. The US would be his great recruiting sergeant. An asymmetric, David-and-Goliath struggle would be transformed into a clash of civilisations. That, at least, was the project.
And that is why the US response always had to be as much political as military, as its many European friends warned. The friction between old allies over Iraq and the shambles there now, the emasculation of the UN, the laissez-faire approach to the Middle East peace process, no less than the discrediting of the political process in the US and Britain as the manufactured excuses for war were exposed are all grist to the bin Laden project and poison to our common democratic project.
Two years on, the legacy of 9/11 is still in the balance.