He dunt wilt. Translation: you may not like him, but he's tough

He got there first this time. Four years ago, Tony Blair was miffed not to be the first foreign leader to shake the new US president's hand. He did not mind being beaten by Vicente Fox, president of Mexico, so much - that was simply an extension of domestic US politics, the reorientation of the Republican polity towards the Hispanic world. It was the fact that Jacques Chirac managed to get to Washington before he did, through some hoquey-poquey diplomatique, that really irked.

He got there first this time. Four years ago, Tony Blair was miffed not to be the first foreign leader to shake the new US president's hand. He did not mind being beaten by Vicente Fox, president of Mexico, so much - that was simply an extension of domestic US politics, the reorientation of the Republican polity towards the Hispanic world. It was the fact that Jacques Chirac managed to get to Washington before he did, through some hoquey-poquey diplomatique, that really irked.

No sign of the old cheese-eating surrender monkey this time, the Prime Minister might have muttered to himself as he got off the plane in Washington, looking over his shoulder. Easy to portray Blair as a general fighting the last campaign, the only politician on the planet who has not realised that being seen with George Bush is a form of electoral aversion therapy back home. Easy to mock his trip to the White House as a campaign tour on behalf of the Liberal Democrats.

But what choice does he have? It is all very well Blair's critics, including his backbenchers and this newspaper, drawing up shopping lists he should take to Washington on the assumption that having 9,000 British troops in Iraq entitles him to bang the Oval Office table and demand "payback". On climate change, Africa or the Israeli-Palestinian peace process, President Bush is unlikely to do anything he would not have done anyway - which in most cases is nothing. The closest Blair got to payback was when, at their joint news conference, Bush emphasised the creation of a Palestinian state. But he managed to make it seem as if that would be on America's terms, or not at all. If the Palestinian people elect the right leader, the US would help them, Bush seemed to say, but if not, not. Even if the "ordinary, decent" people of Palestine, as Blair described them in one of several moments of bathos, elected a committed democrat with whom the US could do business, it must be doubted whether Bush would ever use America's economic leverage to put pressure on the Israeli government.

Similarly, whatever happened in their private discussions, Blair is unlikely to have got much change out of Bush on climate change. The President's main contribution to the great debate about global warming so far, in his State of the Union address last year, was to hail the coming of the "hydrogen economy". The scientific illiteracy of the speech was barely noticed, because hydrogen fuel cells are poorly understood, despite the appearance of fuel cell buses on London streets. All you need to know is that hydrogen is basically a battery. It can be used to store energy and to power things such as buses without producing pollution as the bus moves along. But it cannot generate the energy in the first place - that has to be produced by burning fossil fuels, or by nuclear power stations, or by wind, water or tide. Bush has not even begun to engage with the issue.

All that Blair did get as payback, therefore, was warm words - very warm words - from the chief source of his unpopularity at home. "When times get tough, he dunt wilt," said the President in his fake Texan dialect, and a little part of many Britons watching wilted. The body language of the two leaders was the reverse of previous engagements: it was Bush who was animated and confident, with the wind of election victory at his back; Blair a little stiff and hesitant. It was the latest instalment in the fascinating transformation in our Prime Minister that has been going on for the past two years. In that time he has slowly changed from being one of the most fluid, creative and surprising politicians into one regarded as rigid, inflexible and seemingly trapped by circumstances, having no choice but to plough on.

It all comes down to the invasion of Iraq, to the decisions he took, and did not take, in 2002. They are choices he must replay occasionally in his mind; to ask himself if he could have done anything differently to avert the oncoming train of anti-war righteousness. He appears to believe, sincerely, that he would not have wanted to.

But that is no longer the issue. There may have been alternative histories that could have been written in the period leading to the invasion, but there are none now. In that sense, Blair is quite right about moving on. There seems to be a ruined void at the heart of the anti-war argument. Lenin did not sit in Switzerland saying: "I wouldn't have done that." Or, if he did, he also asked: "What is to be done?" So far, the anti-war tendency can only say it wouldn't have sent the Black Watch to Camp Dogwood; that it wouldn't have attacked Fallujah and that the UN should take over responsibility for security in Iraq. One is tempted to ask: the UN and whose army? The answer given by Alex Salmond, the leader of the Scottish opportunist party, is troops from neighbouring Muslim countries. Such as Iran, presumably. Great idea. In any case, no Muslim country wants to be responsible for running Iraq - and neither does the UN. Kofi Annan, its Secretary General, may be happy to offer the Americans military advice on where and when not to conduct their operations, but he has made it clear that the UN has neither the will nor the resources to conduct them, or not conduct them, itself. So what is to be done, then? No one has come up with an alternative to trying to ensure that Iraqi elections in January are as free and fair as possible - seeing it through, in other words, however difficult and sad the consequences. If there were an alternative, surely millions of people would be taking to the streets of London, Paris and Madrid to demand it.

The absence of an alternative, however, means paralysis, rather than agreement. There is a sullen, bitter acceptance among much of Labour's former middle-class support that Blair will win the next election, but they will not let him move on. Privately, the Prime Minister dismisses them as the "North London intelligentsia" and their equivalents around the country. He affects to be baffled by the difficulty he has in "getting the message across".

But he understands his position and knows that the way to salvage something from his unpopularity is to trumpet it. If you haven't got an alternative, you might as well make a virtue of consistency. Thus his payback from President Bush was nothing to do with the Middle East; it was this: "What the world needs is rock-steady leaders who stand on principle." Tolerate Bush or loathe him, most people would agree with the sentiment. One of Blair's advisers put it to me simply: "It's a strength thing." If Blair cannot be liked, he can be respected. The transformation is complete. Once derided as a man who told everyone what they wanted to hear, people now say of him that they do not agree with him, but at least they know where he stands. He has finally turned into Labour's Margaret Thatcher.