The shifting winds of the 2008 presidential race, which have already blown front-runners off course in Iowa and New Hampshire, are now whipping candidates with gusts of cold air off the Great Lakes in Michigan.

Tomorrow’s primary in this industrial state of ten million people, which has the highest unemployment rate in America, is being overshadowed by dark economic clouds and a growing fear of nationwide recession.

With the Treasury Secretary, Henry Paulson, giving warning last week of a significant slowdown, Mitt Romney is describing Michigan as the “canary in the mine shaft” whose malaise could soon afflict all America. Yesterday the Republican contender once again promised “novel ideas” to turn around the state’s car manufacturing industry, which has long been in a bad way. At campaign rallies he says: “If I’m President of the United States, I will not rest until Michigan has come back.”

Fresh from his disappointing second-place finishes in Iowa and New Hampshire, Mr Romney is desperate for a win in the state where he grew up, emphasising his “personal commitment” to Michigan and a business record of saving failing companies with, if necessary, drastic surgery.

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Although he insisted yesterday that tomorrow’s primary was not “do or die” for his candidacy, Mr Romney has withdrawn resources from other states and has splashed out $2 million on an upbeat TV advertising campaign for Michiganders — more than four times the combined spending of his Republican rivals.

John McCain is delivering a more sober message, warning voters in this state that he cannot “look them in the eye” and promise that the old jobs will return. He pointedly remarked on Saturday that his victory in New Hampshire over Mr Romney last week was because “I told people what was true”.

Mike Huckabee triumphed in Iowa with a message aimed at the evangelical Christian vote, which carries some sway in Michigan too — particularly in the west, near Grand Rapids. But he is seeking to combine this with a measure of economic populism, claiming that Mr Romney is the kind of businessman who sacked a lot of workers.

Yesterday, in a TV interview broadcast from South Carolina, whose Republican primary is on Saturday, Mr Huckabee talked of Michigan’s industrial base being the “arsenal for democracy” in the Second World War, adding: “If we outsource our manufacturing, we outsource our freedom.” Mr Romney’s caustic response was that Mr Huckabee should “stick to things he knows about”, and he attacked the former Arkansas Governor’s record on tax. He told Mr Huckabee, who lacks private sector experience, “don’t cast rocks at people who are trying to create jobs and turn around businesses”.

Missing from this debate are the Democratic candidates who normally would perhaps appeal most to the blue-collar workers shivering in the state’s chilly economic climate.

Their absence is the result of a dispute over Michigan’s decision to move the date of its primary forward from February in the hope of catching national attention. The Democratic National Committee has responded by banning campaigning in Michigan and promising that delegates elected tomorrow night will not be given seats at the presidential nominating convention.

Barack Obama and John Edwards have removed their names from the ballot paper. Hillary Clinton has not. She is expected to pick up the bulk of the 128 delegates — more than Iowa and New Hampshire combined — if the party’s leaders decide not to risk alienating a pivotal state and lift the punishment before the summer convention.

Many Democrats are expected to switch over in this “open primary” in which voters can take part in either party’s contest. Bill Ballenger, of Central Michigan University, believes this should help Mr McCain, who in New Hampshire showed his capacity to appeal to centrists and independents.

But some are being encouraged to play mischief with the Republican ballot. Markos Moulitsas, founder of a liberal website called the Daily Kos, is telling his readers to vote for Mr Romney because the Republican Party “deserves the very worst”. He says: “We want Romney in, because the more Republican candidates we have fighting it out, trashing each other with negative ads and spending tons of money, the better it is for us. We want Mitt to stay in the race, and to do that, we need him to win in Michigan.”

LaMar Lemmons, a state representative in Michigan, has founded a group called “Democrats for Huckabee”, arguing that this would damage a “Republican establishment [which] supports Romney and McCain”.

Still more groups are campaigning for an “uncommitted vote” tomorrow, hoping to elect delegates who could swing against Mrs Clinton, and back — probably — Mr Obama at the convention. Christina Montague, who is organising an uncommitted vote for Mr Obama, has staged rallies and canvass drives seeking to turn out Democrats for a “none of the above” campaign. “We’ve been knocking on doors, we’ve been to barber shops and beauty parlours and sticking fliers on windshields,” she said yesterday.

But Mr Ballenger reckons that most Democrats will either stay at home or take part in the Republican contest, saying: “This uncommitted thing is a bit hard for people to get their heads around.” He suggested that Mr Obama had made a “huge mistake” by removing his name from the ballot. “Everybody thinks that the delegates chosen here will eventually be allowed to take part in the convention. About one third of the Democratic vote is African-American. It’s hard not to think that if Obama was standing, he would have won.”

It would be another twist in this most unpredictable of presidential races if Democrat voters were to bolster Mr McCain in the Republican race - and spell doom for Mr Romney in his home state of Michigan.

Nor is it entirely impossible that Mr Obama’s decision to absent himself from tomorrow’s primary could yet mean the difference between winning and losing the Democratic nomination.

And for the moment, no one quite knows whether it is the cold water of a failing local economy or feverish political machinations which will count most in voters' minds tomorrow night.

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