Mitt Romney headed to Ohio on Wednesday to campaign in the Midwestern state that could make or break his struggling campaign for the Republican nomination next week and decide the presidential contest this November.

Fresh from primary victories in Arizona and Michigan, although still dogged by doubts over his candidacy, Romney was hosting a rally in the auto industry heartland of Toledo.

No Republican has won a presidential election without carrying Ohio and the results there tend to be nail biters.

But before the GOP tries to wrestle the state from President Barack Obama, the party's squabbling candidates must conduct their own showdown on Super Tuesday, when Ohio will be the most important of 10 states up for grabs.

A convincing result could finally seal the deal for Romney, who despite lavish spending on advertising and backing from many in the party hierarchy, remains unable to shake off a continuously shifting cast of rivals.

Rick Santorum, the ever-more conservative former senator from Pennsylvania, already campaigned in Ohio on Tuesday and the two were expected to hammer at each other across the state over the coming days.

While Santorum lost Michigan by three points on Tuesday, he says his strong performance proved that millionaire businessman and former Massachusetts governor Romney is highly vulnerable in Ohio, which has a similar make-up to Michigan.

Michigan was meant to have been easy for Romney, because his father was once governor there, and he outspent the Santorum campaign by 6:1, Santorum spokeswoman Alice Stewart told CNN.

And not only did he fail to win big, but under the complex rules allotting delegates that candidates take to the party convention, Romney may well have come out equal to Santorum, or even behind, Stewart said.

"We're very satisfied with that. The key take away message of this is the delegate count and we gave him a run for his money in that regard. This is not about necessarily who came in first here, it's who's walking away with the most delegates," she said.

Santorum, running on an ultra-conservative platform including a strong stand against abortion and what he considers the excessive separation of church and state, fancies his chances in a state with a hefty blue-collar contingent.

Romney, plagued by gaffes showing him out of touch with the poor and widely seen as a slick technocrat, rather than a people politician, will have his work cut out.

An immediate problem in Ohio is his high-profile position against the government bail-out that saved the US auto industry from collapse in 2008.

Finding a way to stick to his argument -- that the government should never meddle in the economy -- while not alienating the many voters dependent on auto jobs will be key.

On Wednesday, Romney's campaign highlighted endorsements from a group of Ohio manufacturers, who painted the businessman as the one with the "experience" to manage America's ailing economy.

That claim to business savvy is a central part of the Romney campaign and has worked for him in previous primaries, where the man bidding to be America's first Mormon president avoided social issues and focused on jobs.

"Mitt Romney will put Americans back to work," David Johnson, the CEO of Summitville Tile and a former head of the Ohio Manufacturers Association, said.

Santorum, meanwhile, is expected to continue his fiery attacks on social issues that he says mark him out as the only true conservative in the primary race and a stark contrast to the liberal Obama.

And adding to the likelihood of a bare-knuckle week is the reentry of Newt Gingrich, who mostly sat out the Michigan race, but is competing fully in Ohio.

Recent polls show Romney trailing in four of the Super Tuesday states -- Ohio, Oklahoma, Georgia and Tennessee, battlegrounds with a total of 243 delegates.