It has taken more than three years, the loss of tens of thousands of Iraqi and US lives, and US$200 billion - 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 about-face has spread across the conservative spectrum, from William Buckley, venerable editor of The National Review to Andrew Sullivan, once editor of the New Republic.

The patrician conservative columnist George Will now concludes that all three members of the original "axis of evil" - Iran, North Korea and Iraq - "are more dangerous than when that term was coined in 2002".

Neither Buckley nor Sullivan concedes that the decision to topple Saddam was intrinsically wrong.

But "the challenge required more than [President George W. Bush's] deployable resources", the former sadly recognises. "The American objective in Iraq has failed."

For Sullivan, today's mess is above all a testament to American over-confidence and false assumptions, born of arrogance and naivete. But he, too, asserts, in a column in Time magazine, 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, he argues, is fatally poisoned.

This is apostasy on a grand scale. 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 hostile regimes and promoting freedom and democracy.

Its goal was "an international order friendly to our security, prosperity and values". The war on Iraq was the theory's test. And after Iraq, why not Syria, Iran and anyone else who stood in Washington's way?

That doctrine, Fukuyama acknowledges, has been a tragic conceit.

Fukuyama, of course, once claimed in his The End of History and the Last Man, that the world was on a glide-path to liberal, free-market democracy. But he also pointed out that it should have been left to its own pace.

The neo-cons' first error was impatience. The second was a belief that an all-powerful US would be trusted with "benevolent hegemony".

The third was the overstatement of the threat posed by radical Islam to justify the doctrine of preventive war.