As the four remaining Republican presidential candidates reached the most consequential voting day yet, each sought Tuesday to achieve a breakout moment that so far has proved elusive.

The two leading contenders, locked in a dead heat in Ohio, spread out across this marquee Super Tuesday battleground in an effort to reinforce doubts about each other. Mitt Romney argued that he is the only candidate who could fix the economy “because I’ve actually been in it,” while Rick Santorum tried to raise fresh concern about Romney’s conservative credentials.

The 10 states voting Tuesday could help provide clarity for a race that has moved from one would-be Romney challenger to the next. The latest of those is Santorum, who is trying to take advantage of the strength he has built over the past month and prove that he can mount a sustained challenge.

With more than 400 delegates at stake, the Super Tuesday contests offer a significant boost in the quest for the 1,144 delegates needed to secure the GOP presidential nomination. The states voting Tuesday are Alaska, Georgia, Idaho, Massachusetts, North Dakota, Ohio, Oklahoma, Tennessee, Virginia and Wyoming.

Santorum feels the most pressure in Ohio, where the former senator from Pennsylvania built a lead by highlighting his blue-collar roots but where Romney is now considered to have greater momentum.

Santorum left the campaign trail in Ohio and traveled to Washington, D.C., on Tuesday to address the American Israel Public Affairs Committee, while Romney spoke to the influential pro-Israel lobbying group by video link from the Buckeye State. Former House speaker Newt Gingrich also addressed the group by video connection.

After weeks of being sidetracked by discussions about contraception, education and other issues, Santorum returned Monday to his criticism of Romney’s conservative record. He questioned whether conservative voters can trust Romney, highlighting the former Massachusetts governor’s health-care law in that state.

“The underlying problem that I hear when I talk to people all over — they say they just don’t trust Mitt Romney to not do what’s the fashionable thing at the moment,” Santorum said in a conference call with reporters. He argued that Romney had shifted with the political winds on issues including global warming and the individual mandate in his health-care plan.

Romney emphasized his economic message and business experience as key to taking on President Obama in the general election. Romney hopes a win in the quintessential swing state of Ohio might finally rally reluctant Republicans around his candidacy.

“I hope that I get the support of people here in Ohio tomorrow, and in other states across the country,” Romney said at a town hall meeting in Youngstown. “I believe if I do, I’ll get the nomination. And then we can start organizing our effort to make sure that we replace President Obama.”

Romney, who with Sen. Rob Portman (R-Ohio) toured a factory in Canton that makes highway guardrails, said: “What I know is the economy. I’ve spent my life in the real economy. I understand why jobs come and why they go. 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.”

Complicating Santorum’s bid to become the last remaining Romney rival is Gingrich, who is heavily favored to win his home state of Georgia and is banking on victories there and perhaps in Tennessee to revive his candidacy.

Gingrich showed no signs of slowing down and rejected any suggestion that he may drop out of the contest. Addressing overflow crowds in Tennessee, he rallied supporters by pledging that he would bring the price of gas below $2.50 a gallon.

“Tuesday is going to be a mixed bag, and I think the race will go on,” Gingrich said on CNN. “There won’t be any decisive winner Tuesday.”

The stakes are also high for Rep. Ron Paul (Tex.), who campaigned in Idaho on Monday after stumping in Alaska on Sunday. His hope is to marshal loyal supporters in those two sparsely populated states to record his first primary victory of the year.

Romney, meanwhile, is hoping to win enough delegates in Tuesday’s contests to break away from the field. Aides said he anticipates winning a majority of the roughly 400 delegates up for grabs. He campaigned Sunday in Georgia and Tennessee, where other candidates are favored to win, because he could gain delegates that are awarded proportionally.

Monday in Ohio, Romney campaigned as a front-runner, repeatedly touting new endorsements from House Majority Leader Eric Cantor (Va.) and other leaders in the party establishment as evidence of a Republican consolidation.

Polls over the past couple of days show Romney opening a double-digit lead nationally. Surveys also show that he has the momentum in Ohio, although the race here remains essentially tied.

A Quinnipiac University poll released Monday shows Romney leading Santorum by 34 percent to 31 percent — within the margin of error. The same survey a week ago had Santorum leading Romney by 36 percent to 29 percent. A second poll released Monday, by Suffolk University, also showed the Ohio race within the margin of error, but with Santorum at 37 percent and Romney at 33 percent.

Romney’s advisers believe he is building support in Ohio because of a disciplined focus on the economy. “He’s boots on the ground in Ohio, conducting events, spreading his pro-jobs message,” senior adviser Eric Fehrnstrom told reporters. “He’s not like other candidates, who get distracted by non-economic issues. He stays focused on the economy, and I think that more than anything else explains why he’s surging.”

Still, Romney’s team tried to tamp down expectations in Ohio, dismissing any suggestion that the candidate can’t afford to lose but arguing that a Santorum defeat would be harmful.

“I think it’s more damaging to Rick Santorum if he doesn’t win, because he’s been up even double-digits in the polls as recently as last week,” Portman told reporters. “So, the expectation is that Santorum will do very well here. And if he does not, then I think it’s more difficult for him to make the argument that he is able to win enough delegates to be the nominee.”

Staff writer Amy Gardner in Tennessee contributed to this report.