John Rentoul: Beware the playground chants of 'Liar! Liar!'

The most extraordinary development of the final phase of the campaign has been the cynicism of Michael Howard

The strange alliance of anti-war left and pro-war right has finally got what it wanted. The Iraq war is at the centre of the election campaign. Only it isn't. The question about the war is, surely, whether it was right or wrong. Instead, we are debating the Attorney General's opinion of international law; whether the Prime Minister is a liar; why he is so close to George Bush; how he conducts sofa government through unelected advisers. Everything touching on Tony Blair's decision to join the US invasion, but hardly anything to do with whether it was the right decision or not.

The strange alliance of anti-war left and pro-war right has finally got what it wanted. The Iraq war is at the centre of the election campaign. Only it isn't. The question about the war is, surely, whether it was right or wrong. Instead, we are debating the Attorney General's opinion of international law; whether the Prime Minister is a liar; why he is so close to George Bush; how he conducts sofa government through unelected advisers. Everything touching on Tony Blair's decision to join the US invasion, but hardly anything to do with whether it was the right decision or not.

On Thursday, the inwardness of the British media was striking. While headlines around the world reported the appointment of the democratic government in Iraq, the headlines in Britain were about the leak of the Attorney General's advice from two years ago. It turned out that Peter Goldsmith had said precisely what everyone thought he said. He set out the well-known arguments that military action was contrary to international law - arguments that were exhaustively rehearsed in public at the time - before concluding that a "reasonably arguable case" could be made that it would be lawful. The only revelation was the cool clarity of his prose.

Yet the document was reported in the shrill clichés of investigative journalism as the killer memo, without anyone being clear about exactly how it could be fatal to Blair. The fabric of time seems warped when we read that the Attorney General warned that a court "might well" disagree with him and conclude that the invasion was unlawful. This was seized on as an admission that the case was weak, rather than a lawyer's caution. But what matters now is that the war ended two years ago, and no court has since concluded any such thing.

As the Attorney General points out, UK forces took part in military action in Operation Desert Fox - the bombing of Iraq in 1998 - and in Kosovo "on the basis of advice from my predecessors that the legality of the action under international law was no more than reasonably arguable". The Liberal Democrats and Robin Cook supported war on both those occasions, although the United Nations did not explicitly authorise either of them. The differences between those instances and the 2003 Iraq war are therefore of degree rather than absolutes.

The opponents of the Iraq war too often assume that if something is doubtful in international law, then it must be "illegal". In Kosovo and in Iraq, the UK was pursuing ends agreed by the United Nations, even if it could not agree on the means. I thought Kosovo was one of Blair's finest hours, in which he managed to persuade a reluctant America to use force to stop ethnic cleansing. In Iraq, too, I think Blair made the right decision, although I accept that it may be years before we can be sure. But that is why the formation of Iraq's democratic government seems rather more important than the rehearsing of utterly familiar arguments from two years ago.

And that is why on this issue we should care more about opinion polls in Iraq than in Britain. The Iraqi people seem to think that the war was a price worth paying to get rid of Saddam Hussein, and are optimistic about their future as a democracy.

Blair's tragedy is that many of the political attitudes in this country formed in the period before the war have crystallised and fixed themselves in time. The Iraq war was one of those generation-defining events in politics, like Britain's ejection from the European exchange rate mechanism and the winter of discontent. It has a psychological effect that bears little relation to complex reality. The strength of feeling that the war was wrong is such that many people - crucially including most journalists - cannot believe that any reasonable person could have reached the opposite conclusion.

This means that Blair's stated reasons for joining the war cannot be the real ones. Hence he must be a liar and a poodle of George Bush. He could only have agreed to go along with the US because he had committed himself, in a ceremony involving Christian prayer, Colgate toothpaste and rolled-up trousers at the President's ranch in Texas. But why should he have sold the pass in such a way? At this point, the anti-war argument usually slides off into "it's all about oil" or muttering about neoconservatives. Isn't it less complicated just to accept that he believed it was right?

Equally, it makes no sense to allege that Blair exaggerated the intelligence on Saddam's weapons of mass destruction in order to bolster a decision already made on hidden grounds. If anything, he exaggerated the intelligence because he believed it and sought to persuade others to take the dangers seriously. The intelligence agencies in Britain and the US had convinced themselves that Saddam was hiding something. Blair's was not an unreasonable view. He was not looking for reasons to avoid military action; he had long been convinced that Iraq and the world would be safer if the international community were prepared to use force against Saddam.

Nor, in the anti-war view, can cabinet ministers and MPs possibly have supported Blair's decision unless they had been misled or bullied. Proper procedure must have been short-circuited or abused. Parliament must have been lied to, or - in the weaselly code of the supposedly impartial BBC - the failure to find weapons of mass destruction has undermined "trust" in the Prime Minister. But at least it uses code, rather than joining in the debasement of political language.

The most extraordinary development of the final phase of the campaign has been the cynicism of Michael Howard in trying to use the anti-war poison of the "liar" word for his own purposes. I do not know who leaked the Attorney General's advice, but it is a bit of a coincidence that the Conservatives should have unveiled a poster the day before saying of Blair: "If he's prepared to lie to take us to war, he's prepared to lie to win an election."

Leaving aside the childish use of the L-word, Howard's case fell apart like a two-stage rocket. First, he was forced to say that he had never told a political lie - "as far as I am aware" (he is obviously a lawyer not a lexicographer). Then he tied himself in knots for the benefit of the Question Time audience by saying that he would have supported the Iraq war even if he had known that there were no weapons of mass destruction - in other words, on grounds that were even more tenuously legal than those on which Blair relied. It is bizarre that someone whose threshold for military action was lower than the Government's should accuse Blair of lying to take us to war, when Charles Kennedy, who set the threshold higher, manages to observe the normal courtesies.

But the Conservative leader is not interested in making a coherent case against Blair; he wants to swell the playground chant of liar, liar. It is a desperate last throw to depress the Labour vote. Those who thought the war was wrong should not allow the passion of their belief to assist Howard's tawdry cause.