Every now and then an intellectual movement, a school of social, economic or political thought, jumps the cultural barrier that divides the arid squabbling of university senior common rooms from the saloon bar brawling of everyday political discussion.

In the 1970s it was monetarism that made the switch into the mainstream. An economic theory, rooted in orthodox neoclassical explanations about the causes of inflation, was suddenly as familiar a subject to TV viewers and newspaper readers as changes in the cast of MASH.

Since its complexities were too great to comprehend, most commentators did the safe thing and simply looked at the identities of its principal advocates. These seemed to be readily identifiable right-wing villains, so in the demotic demonology of the day monetarism became shorthand for greedy, heartless conservatives.

In the first years of the 21st century, history will recall that it was neoconservatism that played the role of most despised and least understood intellectual theory. For years it languished in the obscurity of certain US universities and think-tanks. Though its adherents were important protagonists in the Cold War, it never really got much of a public airing as a theoretical system of its own.

It took, improbably, the arrival of George Bush in the White House and September 11, 2001, to catapult it into the public consciousness. When Mr Bush cited its most simplified tenet — that the US should seek to promote liberal democracy around the world — as a key case for invading Iraq, neoconservatism was suddenly everywhere. It was, to its many critics, a unified ideology that justified military adventurism, sanctioned torture and promoted aggressive Zionism.

Almost as suddenly as it emerged from obscurity, neoconservatism seems to have collapsed. As the misery in Iraq has deepened, as President Bush and the Republican Party have stumbled deeper into the mire, and as Britain and Europe seem eager to move quickly towards a kind of social democratic system that seeks an all-encompassing multicultural accommodation, the neocons look routed.

It is not just by the Left that the ideology has been rejected, either. The only even vaguely neocon candidate for the Republican presidential nomination, Senator John McCain, is in deep trouble. Britain’s Conservative leader has explicitly rejected neoconservatism.

This is not the place, and I am certainly not the person, for a detailed philosophical study of the ideology. Instead, let’s take the most compelling case against it as a guiding principle for foreign policy: that the war in Iraq has demonstrated beyond a doubt the grotesque naivety of its main thrust.

First, that you can, simply by the exercise of military and other forms of hard power, bring the blessings of liberal democracy to any part of the world. And secondly that, as matter of national security exigency, you should strive to do just that since only a world of liberal democracies will in the end guarantee peace and stability. Iraq doesn’t, it must be admitted, look good on either count.

The US has failed to bring real democracy there, despite losing more than 3,000 troops and spending more than $500 billion. An election or two won’t really cut it — there is nothing civil about the society that now exists in Iraq.

The second count looks even worse. The attempt to push for democracy in Iraq has clearly not been in the US national interest, has not made things more peaceful and stable. The democracy that exists after a fashion in the region — in the Palestinian territories, say, or in Pakistan — doesn’t bode too well for the idea of peace and stability, either.

Some neocons continue to defend the Iraq war on the ground that the idea was right but the execution was disastrous. This blames everything on Donald Rumsfeld, and, increasingly, on George Bush, for not providing resources for the struggle commensurate with the challenge.

This is not really honest. While few would deny that the Bush Administration has produced a textbook example of how not to pursue regime change, most of those who now criticise the White House were not sounding a warning four years ago, when Baghdad fell, that the US needed a vast increase in its commitment.

A more honest judgment would have to be that neoconservatives and their sympathisers — yes, me — badly underestimated the scale of difficulty of effecting radical change in a country such as Iraq. It’s no good blaming either Bush-Rumsfeld or Iraqis themselves. The fact is, the war’s opponents had it right when they said the US would not be able to pull that brutalised, fractious country into the community of civilised states.

It was an error of judgment and not to acknowledge that is to dodge responsibility for the massive daily suffering of the Iraqi people. I still do not think, however, that the basic neoconservative diagnosis was wrong: that the course of history in the Middle East needed a radical change if the world were not to suffer an even greater misery.

The “realists” may have been right that toppling Iraq would lead to instability, but you can’t look at the history of the past 50 years, with its tyrannies and religious fanaticism, and think that in the long term this was sustainable without many more violent clashes with the West.

In the end, the rise and fall of neoconservatism in government may prove not unlike that of its predecessor in the obscure ideology-turned-official-policy stakes, monetarism.

Monetarism was discredited as policy because, while it offered the correct analysis, it failed as policy. I suspect the same will be said for the much derided, little-lamented neoconservatism. It would be foolish if the US tried to do again what it tried in Iraq. But it would be even more foolish to believe that ridding the world of tyranny is itself a mistake. The essence of good policy is fixing the right means in the right circumstances to that end.

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