The Iraq War has left Labour and the Tories on the defensive

To say that this was the week when the 2005 election campaign caught alight is perhaps an exaggeration: the failure of the main party leaders to capture the attention of the voters and provoke a genuine national discussion is a continuing, and regrettable, fact. It is nonetheless true that the campaign looks very different at the end of the week from the way it looked at the beginning - and mostly because the unspoken issue of the first two weeks can no longer be ignored.

To say that this was the week when the 2005 election campaign caught alight is perhaps an exaggeration: the failure of the main party leaders to capture the attention of the voters and provoke a genuine national discussion is a continuing, and regrettable, fact. It is nonetheless true that the campaign looks very different at the end of the week from the way it looked at the beginning - and mostly because the unspoken issue of the first two weeks can no longer be ignored.

The war in Iraq has dominated the week, along with questions about the Prime Minister's judgement. From the first authoritative report of the Attorney General's legal advice and the embittered defection of Brian Sedgemore to the release on Thursday of the complete text, the Prime Minister was forced on to the defensive. The Labour campaign, once so slick and professional, lost the initiative; all its best efforts to divert attention to education, health and the economy came to naught, as Mr Blair was pummelled over Iraq. It is now central to the outcome of this election, as it should have been all along.

The changed focus of the campaign left the Conservatives scrambling. Their decision to support the war - Mr Blair's war - under their previous leader was shown up as the liability it always was. Michael Howard's reaction to the release of the legal advice was nonetheless extraordinary. Rather than exploit its ambivalence to qualify the Tories' support for the war, Mr Howard tried to outperform the Prime Minister as a warrior, inventing "regime-change plus" to define what a Tory government would have done - sans weapons of mass destruction, sans UN resolution, sans legal support. So ill-conceived did this stance appear that successive interviewers on successive days asked him to repeat his answer in case they had misheard. With new Tory posters denouncing Mr Blair as a "liar", the message the party was sending seemed confusingly mixed.

The return of Iraq to the British political arena, on the other hand, revived the campaign of the Liberal Democrats just in time. Boosted by Mr Sedgemore's pledges of support, Charles Kennedy looked a new man. His claim that the party had always planned to raise the war in the later stages of the campaign may or may not be credible, but he presented his party's strongest suit with consistency and confidence.

Nowhere was the change in the leaders' fortunes more evident than on the special edition of BBC1's Question Time. Well-briefed, incisive and friendly with it, Mr Kennedy deserved to win over at least some of those voters hitherto concerned about his competence. Coolly formulaic, Mr Howard had lost much of the verve that had distinguished the early stages of his - largely solo - campaign. Mr Blair looked tired, though still the consummate performer. He persisted in his Luther-like stubbornness over Iraq, tried to steer discussion towards public services and fell at once into a hole of his own making over GP appointments.

Except that such everyday "trivia" have as much potential to galvanise voters as issues of high principle, such as the war in Iraq. Mr Blair's difficulty is that on both levels he now looks out of touch with large segments of the electorate. Will he recover his campaigning magic? Will Mr Howard's gamble on the personal invective pay off? Will Mr Kennedy and his Liberal Democrats be rewarded for their opposition to the war, or will their civil liberties agenda prove a liability? We look forward to next week's final instalment of this unusual and volatile campaign.