It has taken more than three years, tens of thousands of Iraqi and American lives, and $200bn of treasure - all to achieve a chaos verging on open civil war. But, finally, the neo-conservatives who sold the United States on this disastrous war are starting to utter three small words. We were wrong.

The second thoughts have spread across the conservative spectrum, from William Buckley, venerable editor of The National Review to Andrew Sullivan, once editor of the New Republic, now an influential commentator and blogmeister. The patrician conservative columnist George Will was gently sceptical from the outset. He now glumly concludes that all three members of the original "axis of evil" - not only Iran and North Korea but also Iraq - "are more dangerous than when that term was coined in 2002".

Neither Mr. Buckley nor Mr. Sullivan concedes that the decision to topple Saddam was intrinsically wrong. But, "the challenge required more than [President Bush's] deployable resources," the former sadly recognises. "The American objective in Iraq has failed. "For Mr. Sullivan, today's mess is above all a testament to American overconfidence and false assumptions, born of arrogance and naïveté. But, he too asserts, in a column in Time magazine this week, that all may not be lost.

Of all the critiques however, the most profound is that of Francis Fukuyama, in his forthcoming book, America at the Crossroads. Its subtitle is "Democracy, Power and the Neo-Conservative Legacy" - and that legacy, Mr. Fukuyama argues, is fatally poisoned. This is no ordinary thesis, but apostasy on a grand scale.

Mr. Fukuyama, after all, was the most prominent intellectual who signed the 1997 "Project for the New American Century", the founding manifesto of neo-conservatism drawn up by William Kristol, editor of the Weekly Standard, the house journal of the neo-conservative movement. The PNAC aimed to cement for all time America's triumph in the Cold War, by increasing defence spending, challenging regimes that were hostile to US interests, and promoting freedom and democracy around the world. Its goal was "an international order friendly to our security, prosperity and values".

The war on Iraq, spuriously justified by the supposed threat posed by Saddam's WMD, was the test run of this theory. It was touted as a panacea for every ill of the Middle East. The road to Jerusalem, the neo-cons argued, led through Baghdad. And after Iraq, why not Syria, Iran and anyone else that stood in Washington's way?

All that, Mr. Fukuyama now acknowledges, has been a tragic conceit. Like the Leninists of old, he writes, the neo-conservatives reckoned they could drive history forward with the right mixture of power and will. However, "Leninism was a tragedy in its Bolshevik version, and it has returned as farce when practiced by the United States."

But, was it not Mr. Fukuyama who claimed in his most celebrated work, The End of History and the Last Man, that the whole world was locked on a glide-path to liberal, free-market democracy? Yes indeed. But, that book, he points out, argued that the process was gradual, and must unfold at its own pace. But, not only were the neo-cons too impatient, a second error was to believe that an all-powerful America would be trusted to exercise a "benevolent hegemony". A third was the gross overstatement of the post 9/11 threat posed by radical Islam, in order to justify the dubious doctrine of preventive war.

Finally, there was the blatant contradiction between the neo-cons' aversion to government meddling at home and their childlike faith in their ability to impose massive social engineering in foreign and utterly unfamiliar countries like Iraq. Thence, sprang the mistakes of the occupation period.