But where Santorum's boosters see a man with a unique ability to pierce Romney's home-state armor, Romney backers see just the latest fly in the front-runner's ointment -- one that stands to be swiftly swatted away.
"The polls are making it [seem] a lot closer, but I think when you get right down to it, Romney takes Michigan, and I think he takes it rather strongly," said Oakland County Executive L. Brooks Patterson, the long-serving chief of the county where Romney grew up and one of the GOP establishment's biggest power brokers.
Gary Wolfram, a Hillsdale College professor active in Republican policy circles, said he was "90 percent positive" Romney would prevail in Michigan.
Santorum is enjoying a momentary boost mostly because voters simply don't know much about him, Romney's backers reason. Once they find out more -- through daily conference calls with the media and a barrage of nasty television ads -- they'll realize that Santorum, with his career in the dreaded Washington establishment and his history of support for earmarks and government spending, is far from a pure conservative.
"Right now, Rick Santorum is a blank slate out there," said state Rep. Aric Nesbitt, referring to areas like his district in southwestern Michigan near Kalamazoo. "People don't understand his abysmal record of high spending, voting against cutting taxes, passing earmarks.... As soon as this information gets out, things will absolutely change."
The Romney campaign is airing an ad emphasizing the candidate's ties to the state -- in it, he says, "Michigan's been my home, and this is personal," and reminisces about the glory days of the auto industry. Meanwhile, the super PAC backing Romney, Restore Our Future, is blanketing the airwaves with a spot that concludes, "Rick Santorum: big spender, Washington insider."
Santorum's response is an ad that depicts Romney as a crazed, gun-wielding negative campaigner -- "Rombo." It accuses Romney of trying to hide from his own liberal record and predicts that his negativity will turn off voters. But Romney and his allies don't think Santorum's victim act will get him anywhere.
As when Newt Gingrich came under fire in Iowa and Florida, and adopted an elaborately aggrieved posture, voters, they predict, will see a candidate who can't take the heat.
And while Romney's campaign has focused on attacking Santorum's fiscal record, they predict his far-right views on social issues will trip him up and take him off topic. In New Hampshire, Santorum killed his Iowa momentum by getting drawn into unproductive, angry debates about issues like gay marriage. These days, his opposition to birth control and his views on women's roles threaten take him off topic and make even social conservatives wonder about his electability.
And so, in a Republican primary that's refused to end quietly, a high-stakes moment once again looms. Despite the Romney camp's confidence, it seems clear that his candidacy could be riding on the outcome.
Yob, the Santorum backer, noted that Michigan's primary allots delegates proportionally, so a strong second place finisher will still earn delegates. Romney, with his reputation as a moderate, will have a hard time convincing voters Santorum is insufficiently conservative, he said.
"People are going to see through these attacks," he said. "Anybody who attacks Rick Santorum for not being a conservative has got a problem."
Image credit: Reuters/Joshua Lott