Santorum, a former Pennsylvania senator, is going all out in Ohio in an effort to regain the momentum that slipped away in his loss to Romney in Michigan last week. He had held a sizeable lead in Ohio but Romney has closed that gap.
Obama, meanwhile, is seeing his poll numbers rise in tandem with signs that the struggling U.S. economy may finally be on a course toward sustained recovery. A new NBC-Wall Street Journal poll released Monday shows him defeating all of the Republican candidates in hypothetical head-to-head matchups.
He also has been helped considerably by the Republicans having been driven badly off their economic message by a detour into a rancorous and nasty debate over whether religious-affiliated institutions – not churches – should be required to offer health insurance coverage for contraceptives.
An uproar, mostly among Catholic leaders who reject contraception on moral grounds, forced Obama to change the birth control mandate. The new plan would require insurance companies that cover workers in religious-affiliated institutions like hospitals and universities – and not the religious organisations themselves – to pay for the contraception coverage.
Just as the contentious issue started to fade a bit, Rush Limbaugh, a conservative radio personality, forced it front and centre once again: The issue has only grown more contentious after he apologised for calling a Georgetown University law student who had spoken out in favour of the Obama plan a "slut" and a "prostitute" who wanted the government to pay her for having sex.
And the issue seemed certain to deepen the concerns of many women voters, who – along with the broad spectrum of all independents – will likely determine the ultimate outcome in the November election. Polls show women are already turning back to Obama.
Romney and Santorum, meanwhile, were fighting it out for every single vote in Ohio.
Speaking to supporters at a guardrail factory in the industrial city of Canton, Romney tried to snap the subject back to the economy and away from social conservative issues.
"I look at this campaign right now and I see a lot of folks all talking about lots of things, but what we need to talk about to defeat Barack Obama is getting good jobs and scaling back the size of government, and that's what I do," Romney said. "Other people in this race have debated about the economy, they've read about the economy, they've talked about it in subcommittee meetings. But I've actually been in it."
Santorum told Ohioans the election must be earned, not "bought," in another swipe at Romney's advantage in funding and superior campaign machine. "Look into what the candidates have overcome and what they offer to this country – not just what money they have, but where's the soul, where's the conviction, where's the fight?" he told hundreds of students and supporters at Dayton Christian School.
Santorum said that no matter how much Romney spends, "conservatives will not trust him, will not rally around him this primary season. ... We will be the nominee."
Seemingly confident of a primary victory in Georgia, Gingrich unveiled a new television commercial in Tennessee promising to reduce the rising cost of gasoline.
Gingrich linked oil, Iran and war in remarks at a rally in Alcoa, Tennessee. "We should indicate calmly and decisively that any threat to close the Straits of Hormuz would be considered an act of war and we will eliminate the government of Iran," he said. About 20 per cent of the world's oil exports pass through the Straits of Hormuz in the Middle East.
About one-third of the 1,144 delegates needed to clinch the nomination are at stake Tuesday, a larger prize than all the previous primaries and caucuses combined. The nominee will be named in late August at the Republican National Convention in Tampa, Florida.
Obama picked Tuesday to hold his first news conference of the year, a chance to steal a bit of thunder from the Republicans on their big day and defend a record of economic stewardship that is under daily assault in the Republican campaign.
On the eve of Super Tuesday, the message coming from Republican establishment figures was clear: It's time, if not past time, to crystallise the competition and unite the party behind the effort to defeat Obama in the fall.
House Majority Leader Eric Cantor and Sen. Tom Coburn, one of the most conservative members of the Senate, were among the latest Republican luminaries to swing behind Romney. Conservative John Ashcroft, attorney general in the George W. Bush administration and a former Missouri senator, threw his support behind Romney on Monday.
Romney has won four consecutive contests, including Saturday's Washington state caucuses. His broad, well-disciplined organisation all but assures he'll collect more delegates than his opponents on Tuesday. Santorum and Gingrich did not collect enough signatures to qualify for the Virginia ballot, for example, and Santorum cannot win 18 of Ohio's 66 delegates for similar reasons.
So far, Romney leads with 203 delegates from previous contests, Santorum has 92, Gingrich has 33 and Paul, 25.