Columbus, Ohio — In early February, Rick Santorum scored big, winning the Missouri primary and caucuses in Minnesota and Colorado. The sweep came at a critical time. Santorum, who had watched his poll numbers fade in January after Mitt Romney carried Florida and Nevada, desperately needed momentum. But since that trifecta, Romney has surged ahead, winning five straight contests.

On Tuesday, Santorum will once again seek a Rust Belt rebound. If he can take Ohio, he will — in the eyes of GOP consultants — be able to reassert himself as a national contender. “If he wins Ohio, the race keeps going; it becomes a delegate battle,” says Steve Schmidt, John McCain’s former strategist. “But if Romney wins, the Santorum campaign’s best days are almost certainly in the rearview mirror.”

A Reuters/Ipsos poll released on Sunday shows a dead heat in the Buckeye State, with both Romney and Santorum garnering 32 percent support. An NBC News/Marist poll shows similar figures, with Santorum leading Romney by two points, 34 percent to 32 percent.

A Quinnipiac survey released on Friday, however, shows Romney leading Santorum by four points, 35 percent to 31 percent. “Romney is closing strong but Santorum could easily cobble something together,” says one Republican familiar with internal polling. “It’s a toss-up.”

Over the weekend, Santorum played down expectations. After leading by double-digits in a handful of Ohio polls last month, he acknowledged that he faces a difficult test, even though state demographics seem to dovetail with his blue-collar message.

“It’s a tough state for us, if only because of the money disadvantage,” Santorum explained on Fox News Sunday. “We’re hanging in there.”

Or at least he’s trying. On the Ohio airwaves, Romney has dominated. Restore Our Future, a pro-Romney super PAC, has spent over $2 million on ads. Romney’s campaign has spent over $1 million. The Red, White, and Blue Fund, a pro-Santorum super PAC, has spent about $500,000; Santorum’s campaign has spent even less.

Santorum may blame an Ohio defeat on money, but it will not dampen the damage of such a loss, says Dave Carney, a veteran GOP politico and Rick Perry’s former strategist. “It would really hurt his rationale for running,” he says. As a candidate who “talks about populism and who says he understands manufacturing culture,” he needs to win here, period.

To boost his chances, Santorum will stump throughout Ohio on Monday and Tuesday, holding rallies near industrial centers in Miamisburg and Cuyahoga Falls. On Tuesday, he will watch the returns from Steubenville, a small city near the Pennsylvania border and the home of Franciscan University, a Roman Catholic college.

Santorum staffers, for their part, are confident that they can turn out their supporters. They have poured resources into mailings, and campaign manager Mike Biundo has spent much of his time over the past month on the ground in Ohio, coordinating outreach and volunteers.

“In Cincinnati, in eastern Ohio, in the factory towns — we see opportunity in a lot of places,” says one Santorum adviser.

But the pressure to win is intense — not necessarily for the delegate count, but for the energy that would come with a swing-state victory.

In fact, due to missed filing deadlines, Santorum is ineligible for a slice of Ohio’s 60-plus delegates, which will be awarded proportionally.

Still, as GOP observers see it, those numbers will be important on Tuesday, but not everything. Santorum, many say, needs to first clinch the popular vote in Ohio before he worries about a long delegate war.

“It’s a question of staying alive,” says Sal Russo, a former aide to Ronald Reagan and an adviser to the Tea Party Express. “If you don’t have the national muscle, you need to win places like Ohio to sustain your campaign. The whole process favors a candidate like Romney who has the organization. Without that, you need fresh success.”

As he campaigned in Tennessee on Sunday, Santorum told reporters that he needed to “narrow” the GOP race down to two candidates. “I think that will happen eventually,” he said. “This is a game of survival.”

Indeed, Santorum advisers are hoping that an Ohio win would help to nudge out Newt Gingrich, who will likely win Georgia on Tuesday. But that won’t be easy. Gingrich is a defiant politician who has pledged to fight on should he win the Peach State. And should Santorum stumble in Ohio, Gingrich would likely see ample reason to do just that.

“If Romney wins Ohio, the game is over,” says Ed Rollins, a former Reagan adviser who managed Michele Bachmann’s presidential campaign. “The momentum would be with Romney, with Newt hanging in. It’d be tough for Santorum to get that momentum back.”

— Robert Costa is a political reporter for National Review.