For most of the last three years, John McCain has not missed an opportunity to tell anyone who would listen that the war in Iraq was being mismanaged by the Pentagon, that Donald Rumsfeld was doing a terrible job as Defence Secretary, and that the US needed to recommit itself to winning the war with more troops and a new strategy aimed at defeating the insurgency.

But as his campaign for the Republican nomination for the presidency gets seriously under way, he must be ruefully reflecting on that old adage: "Be careful what you wish for."

When President Bush fired Mr Rumsfeld last November after the Republican defeat in the midterm elections, it might have seemed that – at last – the administration was listening to the senator's criticisms.

When he followed that up two months later by announcing a bold new strategy – the "surge" of troops to Baghdad – in a much more serious effort to restore order, it looked like further vindication.

But even as the President seemed to accept the logic of Mr McCain's criticism, he has made it much harder politically for the senator to distance himself from an increasingly unpopular war that could derail his presidential ambitions.

Having Mr Rumsfeld to kick around always offered the senator the most practical and easiest way to attack the war's conduct without directly criticising President Bush, something still considered unseemly even in the now fractious Republican Party.

And as long as Mr Bush and Mr Rumsfeld were continuing their bumbling "stay the course" strategy, Mr McCain could say, with real conviction, that this was not his preferred approach, and that, if the administration was not serious about winning the war, it might be better if the US pulled out completely.

But with Mr Rumsfeld gone and the surge now under way, the US now appears firmly committed to what the Democratic contender John Edwards cleverly christened "the McCain Doctrine".

This spells trouble for Mr McCain if he is to win the presidency next year. If the new strategy does not succeed in quelling the violence, it is hard to see how the senator can win a general election against a Democrat.

Mr McCain is still frustrated by the administration's actions. Those close to him express strong doubts about the administration's new strategy – which they think involves not enough troops, deployed too slowly to Iraq, with confusing signals about how long they will be kept there.

But in public Mr McCain is now the loyal supporter. In political terms he needs to ensure that the blame is attached not to him for his support for the war, but to those who in his view have mismanaged it for the last few years.

That was why – most unusually for a Republican – he voted against the appointment of General George Casey, the US commander in Iraq for the last two years, as the army's chief of staff

And that was why he was unusually vocal on Monday in a speech in South Carolina in his criticism of Mr Rumsfeld, describing him as "one of the worst defence secretaries in history".

Mr McCain's advisers still believe his association with the war will not destroy his prospects in the Republican primary. They continue to argue that no serious Republican will run on an antiwar platform. Instead, they say, Republicans will be looking for real evidence of leadership and competence in national security – something Mr McCain offers in spades

Republican voters will also be looking for something else – a real and effective means to attack resurgent Democrats. Which was why Mr McCain, in addition to his verbal assault on Mr Rumsfeld on Monday, had some contemptuous remarks for Democrats. He described their efforts in Congress at the weekend to pass resolutions condemning the conduct of the war as "a charade and a joke and a publicity stunt".

The more the senator can turn Republicans' anger onto the Democratic Party, the better his chances of winning them over.

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