But Mr Vilsack had better enjoy his brief, solitary moment in the spotlight. In the next few months a host of stronger candidates in both parties will muscle in on what could be the most hotly contested presidential campaign in decades. The midterms not only cast a shadow over George Bush’s presidency, they provided useful early pointers to the identity of his successor.

Democrats had most cause to celebrate, of course, and the results on Tuesday probably did nothing to dislodge Hillary Clinton from her perch as the firm favourite for the party’s nomination. She won her own Senate contest in New York with two thirds of the vote and raised more money than any other candidate in the country. One small tea leaf signalled a little concern for her: Democrats had hoped to grab as many as six Republican seats in the House of Representatives in conservative upstate New York, which would have been a fillip for Mrs Clinton’s credentials as a centrist. But they ended up with just three gains.

Barack Obama, one possible alternative, wasn’t up for re-election but his profile grew exponentially during the campaign and, should he run, the black senator from Illinois will be a favourite to upset Mrs Clinton. The midterm results could have been slightly better for him. Harold Ford, another young, black Democrat, failed in his attempt to win the Tennessee Senate seat. If he had won, it would have given a boost to the idea that a black man could win votes even in once-hostile territory in the South.

One intriguing outcome of the elections was a sharp tilt to the left in Iowa and New Hampshire, the two states that host the first primaries of the voting season in early 2008. In each, Republicans lost two House seats to left-wing, anti-war Democrats. This might suggest that voters there have become more energised and radicalised — which could spell trouble for candidates seeking the centre ground such as Mrs Clinton and good news for people such as John Edwards, the former senator and vice-presidential candidate in 2004, and Russell Feingold, the Wisconsin senator. They have both been running early on a strong anti-war platform and will be spending much more time in the two states in the coming months.

Al Gore may take similar encouragement if he decides to run but the 2006 midterms probably finished off John Kerry after his late campaign gaffe in which he seemed to insult the intelligence of US troops. The only Republican likely to be grinning after Tuesday’s debacle is John McCain, the Arizona senator who is the frontrunner for the party’s nomination.

Mr McCain appeals to the centre ground but is viewed with suspicion by many conservatives who vote in large numbers in the Republican primary. But exit polls on Tuesday suggested that independent voters voted overwhelmingly for Democrats. Republicans will have to focus less on appealing to their conservative base and more on winning over the centre in the next two years and Mr McCain is well placed to do that.

One other factor worked in his favour this week. Democrats advanced strongly in the mountain west of the US, winning a Senate seat in Montana and House seats in Colorado and Arizona. That part of the country may well become a critical battleground in 2008 and Mr McCain, a local boy, might prove irresistible. One danger for him, though, is the unpopularity of the Iraq war. Mr McCain has been one of its most fervent advocates.

Among other Republicans Mitt Romney, the outgoing Governor of Massachusetts with the film star looks, has done a better job of appealing to conservatives than Mr McCain while also maintaining a broad middle-ground appeal. His Mormon faith is still a liability for him in much of the country, however. A possible alternative is Rudy Giuliani, the popular former mayor of New York who was highly visible helping Republican candidates in the past few weeks.

It was a bad week for conservatives but there is still a gap in potential candidates’ ranks for someone who can appeal to that powerful constituency in the Republican Party. With George Allen, the Virginia senator, losing his seat, the likeliest contenders are Newt Gingrich, the former Speaker, Bill Frist, the outgoing Senate Majority leader from Tennessee and Sam Brownback, a charismatic religious conservative senator from Kansas.

As the candidates prepare for the starting gun they will recall that in every presidential election cycle a pattern has been established. The frontrunner in both parties gets off to an early lead and then suffers nearly disastrous setbacks before pulling away to win the nomination. Something to remember if John McCain and Hillary Clinton seem to stumble as they embark on their great adventure.

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