George Bush's state visit to Britain was a photo opportunity for a faltering president planning a hasty exit from Iraq in the run-up to next November's election. With the hideous attacks in Istanbul, it turned into an opportunity to display grim resolution in the face of a ruthless enemy. Flanked by the British Prime Minister as his loyal lieutenant, the President insisted that the atrocities would in no way alter American policies.
We should take Mr Bush at his word. Al-Qa'ida-linked suicide bombers blasting British targets in Turkey will not change America's policies. The war on terror will continue, but against a background of an escalating guerrilla conflict in Iraq. American forces will adopt a harsher stance, using air power to attack suspected terrorist sites, but they will do so as a prelude to a disorderly retreat that will leave radical Islam the single most powerful force in the country. The Iraqi state could break up, leaving the entire region desperately unstable.
The decisive factor in this unfolding catastrophe will not be al-Qa'ida but the exigencies of US politics. There may well now be a majority of American voters who have misgivings about the war, and Mr Bush is not going to risk his chances of a second term in office if he can help it. Aside from the quickening flow of body bags, America's adventure in Iraq is hugely expensive. When it clashes with the imperatives of domestic politics, Iraq is expendable.
Invading and occupying Iraq was never justified by any clear national interest. Since the end of the first Gulf War, Saddam has posed no serious threat to the US or to Britain. No evidence has ever existed of a connection between him and al-Qa'ida - though in the chaos of post-war Iraq the remnants of the regime may be linking up with radical Islamists to attack US forces.
None of the reasons given for waging the Iraq war has ever held water. At the same time, it was always going to be counter-productive in terms of dealing with al-Qa'ida. Fighting terrorism is much more a type of police work than an exercise in conventional warfare. America's armoury of hi-tech weapons ensured a swift victory over Saddam's army, but they are worse than useless in a guerrilla war. By attacking Iraq, the Bush administration has created an ideal environment for terrorism.
The war has only harmed the struggle against al-Qa'ida - as was forecast time and again by diplomats, defence experts and Middle East specialists in the run-up to the war. Why then was it waged? And why did Mr Blair embroil Britain so deeply in it? As far as the Americans are concerned, the answer lies partly in geopolitical calculations linked to oil. In the Prime Minister's case, part of the explanation is his misguided belief that by showing unstinting public support for American policies he can be privately influential in moderating their excesses. Yet I believe a more decisive factor than either of these to be the unprecedented power of neo-conservative ideology - not only in Washington, but also in No 10.
In his Banqueting Hall speech in London the President outlined the Bush doctrine, in which regime change in Iraq is a move in a larger strategy to reshape the Middle East in an American image. Bush plans to export an American version of democracy throughout the Middle East.
It is a grandiose enterprise that has an irresistible appeal for Mr Blair. The Prime Minister's evangelical instincts find little scope in the mundane world of British politics. His role as Mr Bush's cheerleader seems to give him an intoxicating sense of righteousness - while placing him reassuringly on the side of the big battalions. With US power backing his pretensions to world statesmanship, Mr Blair can hope to be remembered for something more than his modest achievements in the domestic arena.
The Prime Minister's hopes are naive. Toppling dictators confers an invigorating sense of virtue, but the alternative to secular authoritarian regimes such as Saddam's Iraq is not democracy, but a populist version of theocracy. The attempt to export democracy will condemn the Middle East to decades of instability and war, with radical Islam being the beneficiary.
As the neo-conservative publicist and Pentagon adviser Richard Perle boasted when he admitted the war in Iraq to be illegal in a recent debate in London, the Bush administration is happy to ignore international law when it stands in the way of US interests. Equally, the President will cheerfully abandon Iraq the moment it becomes an electoral liability. As is shown in his tilt to protectionism over the past year, domestic political considerations take priority over everything else.
In terms of his view of the world, Mr Blair is a neo-conservative. Like his friends in the White House, he sees America as the embodiment of human progress. Unlike them, he does not call the shots. Having followed the Bush administration into an unnecessary and unwinnable war, he must now do its bidding as it prepares to cut and run - leaving Iraq in chaos, the terrorists who struck in Istanbul stronger, and British citizens at greater risk. It will guarantee Mr Blair a place in the history books - but not, I suspect, the one he has in mind.
John Gray is the author of 'Al Qaeda and What It Means To be Modern' (Faber and Faber)