And yet to visit the US at present, as I have done, is to experience an overwhelming sensation of drastic impending change. It's not merely that President Bush, to whom Blair so disastrously tethered himself, is "in office but not in power". Most Americans can't wait for him to go, Congress is beyond his control, and the Senate majority leader, Senator Harry Reid, has told him that the war in Iraq is lost - for which statement of the obvious Reid was accused of "defeatism" by the vice-president, Dick Cheney.

Besides that the portents range from Paul Wolfowitz's travails at the World Bank to the Senate interrogation of Alberto Gonzales, the attorney general, and the trial of Conrad Black. This might sound like the "succession of small disasters, oh trifling in themselves", in Alan Bennett's Forty Years On ("a Foreign Secretary's sudden attack of dysentery at the funeral of George V, an American ambassador found strangled in his own gym-slip...") And yet there really is an observable pattern.

Along with the collapse of Bush's authority, all these episodes are connected to the great disaster in Iraq. And all illustrate the hubristic, impenitent arrogance of the people who have been guiding America's destiny - as well as ours, alas - for the past six years. What one senses so acutely are the conditions building for a political perfect storm, which will engulf and destroy the whole neoconservative project.

In Washington I took part in a debate with Christopher Hitchens, my old sparring partner and drinking companion (mots justes, all of them), who supports Bush with a defiance worthy of a better cause. He surpassed himself by insisting that his friend Wolfowitz is a wronged man. A World Bank committee reportedly disagrees, and has found that Wolfowitz did violate the bank's rules in the matter of his lady friend's salary.

But in any case everyone else in Washington says the same thing: Wolfowitz cannot survive. His appointment was widely resented in the first place - the German, French, Dutch and Scandinavian governments have warned that they might withhold funds if he stays in office; and severe damage is being done to the organisation he claims to have at heart by his refusal to accept reality.

Then again, detachment from reality is perhaps to be expected from one of the architects of the war, a man who thought that the Iraqis would rise up to greet the American army as liberators. As the Nobel-winning economist Joseph Stiglitz said, Wolfowitz and his cabal "do not seem to understand that being president of the World Bank is a privilege, not an entitlement".

Gonzales was just a Texan hack lawyer who acted as Bush's consigliere, but he made his contribution to the great enterprise when he ruled that torture could be justified in the "war on terror". His Senate hearing provided a little comic relief, what with his acute amnesia followed by the deathless admission that "I now understand there was a conversation with myself and the president". One day Blair may understand that there was a conversation between himself and the president about the invasion of Iraq, and that his commitment to the war took place much earlier than he has ever admitted.

While Lord Black has never worked for the Bush administration, he was aligned with the neocon elite through the National Interest, the journal he used to publish, and he brought some of its members, such as Richard Perle, on to the board of his companies. Perle seems to have taken his fiduciary duties as lightly as he and his colleagues took the problems that would arise in Iraq as a result of the invasion. What has struck me about Black's trial was that we were hearing another version of the arrogance and denial we have heard from Wolfowitz and many others. It will give me no particular pleasure if my former employer is banged up, but his downfall is another grave blow for the neocons.

All of which has vital implications for British politics. Nicolas Sarkozy has been called "an American neoconservative with a French passport", which he is not. But Blair really is an American neoconservative with a British passport. He revealingly and accurately said that "there isn't a world of difference" between himself and the neocons politically, and his party must now, as it shakes off the burden of these past years, ask itself what, in that case, he was doing as Labour leader.

The Tories have questions of their own. Even the stupidest have grasped that the war and the American alliance are unpopular with the electorate, but they should now ask if sceptical, pragmatic Conservatism ever had anything in common with neoconservatism and its vast revolutionary scheme. One who did understand is Matthew Parris, the former Tory MP. Before the 2004 presidential election he said he wanted Bush re-elected: his presidency was halfway through an "experiment whose importance is almost literally earth-shattering" and should be played out to its inevitable failure.

But that failure must be demonstrated beyond contradiction. "The theory that liberal values and a capitalist system can be spread across the world by force of arms... should be tested to destruction ... The president and his neoconservative court should be offered all the rope they need to hang themselves."

His wish has come true; neocons are dangling all around us. In a flicker of self-knowledge, Wolfowitz told a recent World Bank meeting: "I understand that I've lost a lot of trust, and I want to build that trust back up." But it's too late, for him and all the other courtiers. They never really enjoyed the trust of most Europeans, let alone Africans and Asians, and they have now lost the trust of the American people.

All the readings on the barometer and the wind gauge say the same thing. The perfect storm is gathering. Unfortunately the collapse of the neocon project comes at a very heavy cost, not only to the people of Iraq but to all of us.

· Geoffrey Wheatcroft is the author of Yo, Blair!

wheaty@compuserve.com