Cuyahoga Falls, Ohio — Rick Santorum came here on Monday night, to a packed town center on the banks of the Cuyahoga River, not merely to stump and shake a few hands, but to plead. “It’s gut-check time,” he told the crowd of several hundred. “Who wants it the most? What do you say?”

The audience roared.

“All of the party chieftains have lined up behind the next guy in line with the most money,” Santorum told them, and he scolded Republican grandees for ignoring a “guy from a little steel town” in southwestern Pennsylvania.

That raw populism drew sympathetic nods, especially from a group of middle-aged industrial workers, many of whom are struggling to find work in northeastern Ohio, a former manufacturing powerhouse.

“We relate,” Santorum said, looking at a burly man in a Cleveland Browns sweatshirt. “Pittsburgh and Cleveland are sister cities.”

Santorum paused and he lowered his voice. He dropped the talk about Mitt Romney, his chief rival, and shelved the barbs about President Obama. He spoke wistfully about the “neighborhoods we grew up in,” where families — not the government — were central. “The sense of community, the importance of family and faith,” all of these things, Santorum said, had lifted America in years past.

If elected, he pledged, he would promote those values in the White House. “That’s the environment that built the strong backbone of America,” Santorum said. “I believe in this area. I believe that the better days are not behind us.”

The passage summed up Santorum’s case to Ohio Republicans, and to all Republicans who are voting today. Santorum casts himself as a blue-collar warrior, a rock-ribbed conservative. To win in November, he tells Rust Belt underdogs, support one of your own.

And to a point, Santorum’s argument resonates. Romney’s campaign is ruthlessly efficient, but a tad bloodless. Earlier Monday, the former Massachusetts governor held a town hall in Youngstown, Ohio, that was lit better than a Hollywood film set. The crowd there — smaller and carefully arranged in rows of folding chairs — lacked the passion of Santorum’s rally.

But that may not matter much when the results are announced tonight. Romney may clinch Ohio, according to the latest polls.

Santorum has energy and spunk, but beyond that, he has challenges. He lacks Romney’s organization, his national fundraising base, and most notably, Romney’s steely discipline.

Yet on Monday, here in this bland room with bad lighting and a live band playing oldies, Santorum did not sound like a man ready to return to the pundit ranks. He was upbeat, fiery, and eager to fight on. He noted that he has been counted out before, only to surge back into contention.

Santorum recalled his Iowa efforts, which resulted in a surprise victory following months of campaigning without fanfare. “We went out and delivered a strong, clear message,” he said. “We needed a conviction conservative, someone who had a record and a vision, not just something to run on — a candidate who understands the plight of everyday Americans.”

Ever since Iowa, through late-January disappointments and early-February elation, Santorum has returned to that theme. He spends time blasting Romney for mandating health-care coverage in Massachusetts, but that has never been the thrust of his campaign. Instead, it all comes back, in every speech, to who he is: the son of a poor Italian immigrant, a father of eight children, and, yes, a former senator, if one who lost big in 2006.

In a sense, Santorum embraces his losses, both the personal and the political. As he told reporters on Monday, he is David versus Romney’s Goliath — an underfunded outsider. He rails not only against liberal economic policies but against the maneuverings of Beltway Republicans. Romney may win every race, he tells conservatives, but he hasn’t won your heart.

Many GOP operatives believe that if Santorum ekes out a narrow Ohio victory, or finishes a strong second, he will have enough fuel to carry on. Wins in Tennessee or Oklahoma would also boost his viability.

But on the trail, what’s striking is that Santorum doesn’t seem to view this contest as a delegate battle, or a nationwide scramble for votes. He is waging a different kind of war. He is attempting, as did Jack Kemp and Pat Buchanan before him in their different ways, to connect the GOP to the working class.

Even if it stumbles, Santorum’s Ohio campaign has highlighted a glaring Romney weakness. Romney may hold tightly scripted town halls in factories; he may talk up his love of cars. But it’s Santorum, the scrappy insurgent, who has clicked with frustrated, Midwestern hard-hat workers.

If Romney wins the nomination, but can’t find a way to enthuse these voters in November, then his primary victories will have been empty ones.

— Robert Costa is a political reporter for National Review.