The crucial battleground: Romney stakes all on a narrow victory in Ohio

On the eve of the biggest day yet in the race for the Republican nomination, Mitt Romney toured a plant here that specialises in galvanising metres of steel in baths of molten zinc to make motorway guardrails. As a piece of campaign choreography it was neat: Team Romney is nothing if not galvanised.

There will be no clean sweep for the former Massachusetts Governor as Super Tuesday dawns today. Not quite half of the 10 states voting risk going to his rivals and Ohio, the most psychologically important of all them, remained hard to project with polls showing him in a dead heat with Rick Santorum. But after weeks of unedifying warfare, the muddle of the 2012 primary contests may be starting to clear somewhat.

"Gosh, we've just won five states in a row," Mr Romney boasted to a polite crowd of 200 in a warehouse of Gregory Industries, steel coils and struts around him. The wins included Washington State at the weekend. And suddenly, if belatedly, he is starting, he said, to garner "the endorsements of key Republicans across the country".

Mr Romney may win more delegates tonight than his three rivals combined. But there may still be blemishes with Mr Santorum and Newt Gingrich looking to hold bastions in the South. And there will be pain for sure if he loses Ohio, a critical piece of the American electoral jigsaw. A new Quinnipiac University poll showed him at 34 per cent to 31 per cent for Mr Santorum in the state.

This may be déjà vu in the making – a week ago Mr Santorum led decently here. But Mr Romney seems to be gaining crucial traction in the last hours to erase that deficit just as he did in January in Florida against Mr Gingrich and in Michigan last week against Mr Santorum. "The margin makes Ohio too close to call but Romney is the one with wind at his back," Peter Brown, assistant director of the Quinnipiac Polling Institute, noted.

Nationally, Mr Romney is doing better, too. A Wall Street Journal/NBC survey saw him regaining the lead from Mr Santorum among likely GOP primary voters, thanks in part to growing support from conservatives. But the survey suggested the internecine primary contests have hurt the Republican field. It saw Barack Obama's approval rating jump to 50 per cent. In a head-to-head match-up today Mr Romney would lose to Mr Obama, 44 per cent to 50 per cent. The poll showed 40 per cent of Americans view Mr Romney unfavourably.

"The problem is they have just been giving ammunition to Mr Obama," said Greg Geraghty, 44, a boiler inspector who came to the Gregory factory to see Mr Romney for himself. Mr Geraghty was still undecided between Mr Romney and Mr Gingrich.

"I don't know why they don't see that and they can't somehow unite," he said.

Super Tuesday: the states that vote

Candidates need to secure the backing of 1,144 delegates at the Republican convention in the summer in order to take on President Obama in November. Tonight, they'll fight it out for delegates across 10 states.

Alaska 27 delegates

Georgia 76 delegates

Idaho 32 delegates

Massachusetts 41 delegates

North Dakota 28 delegates

Ohio 66 delegates

Oklahoma 43 delegates

Tennessee 58 delegates

Vermont 17 delegates

Virginia 46 delegates