Leading article: The eclipse of Bush's brand of messianic conservatism

The results were not quite the double landslide the most optimistic Democrats had hoped for, but they were a signal achievement nonetheless. From January the Democrats will control the House of Representatives with the largest majority either party has enjoyed for years. The United States will have its first woman Speaker of the House and number three in the constitutional hierarchy. Control of the Senate remains in doubt, but there were exceptionally close races in states where Republicans would in most years have banked on victory. All in all, it was an impressive tally for one day of voting.

This result, though, is far more than the sum of its individual contests - as the summary removal of the defence secretary, Donald Rumsfeld, showed. It constitutes a political turnaround comparable to that wrought by the Republicans with their Contract for America in 1994. That victory tapped into the same sentiments that were to facilitate George Bush's contentious victory in 2000. Tuesday night's results mark the eclipse - for the time being, perhaps forever - of that particular brand of messianic, back-to-basics, Republicanism.

And while individual Republicans can be called to account for scandals that cost them their seats and besmirched their party, overall blame for this defeat lies squarely with George Bush - as he acknowledged last night. The Iraq war was central to this campaign. But - as US polling showed - Iraq was not all the campaign was about. It was also about the competence - or rather lack of it - of the administration, about leadership, and how Americans saw their country and themselves.

To the extent that the war was the central issue, it was not simply as a disastrous military adventure, but as the essence and logical outcome of everything George Bush stood for. The war embraced the neo-conservative advisers who reinforced the President's black and white view of the world. It meant the combination of paranoia and hubris that coloured his approach to the world after the attacks of 11 September, 2001. It meant the arrogance Mr Bush showed in defying the UN to force regime change in Iraq and then declaring victory prematurely.

The swift removal of Mr Rumsfeld, and his replacement by Robert Gates - a man of a far less ideological bent - suggests that a change, or at least a shift, in Iraq policy is imminent. Whether it will be timely enough to have any effect, it is still worth recording that we are watching something very rare in the world of politics: the author of a policy that has grievously failed having to face the consequences on his own watch.

How much real power the Democrats will now be able to exercise depends a little on the final result of the Senate vote, and a great deal on how the President and Nancy Pelosi, the new House Speaker, decide to play it. Legislative gridlock, though, is not inevitable. Mr Bush has worked constructively with a Democratic legislature before, as Governor of Texas, and could doubtless do so again. The fact that neither he nor his Vice-President will be running for office again gives him more freedom of manoeuvre, should he decide to use it.

Ms Pelosi, for her part, has said that she wants the Democrats to use their power constructively. A shift of policy on Iraq might help silence Democrats' calls for more inquests into the political decision-making over Iraq and oil the wheels of legislative co-operation.

The real significance of these midterm elections is unlikely to reside in any laws enacted in the coming 24 months. It will be in the adjustments Mr Bush has to make in the hope of saving some dignity in Iraq and in the new personalities and power relationships that will shape the presidential race in two years' time.