TROY, Michigan — The state’s top elected Republican officials took their turns on the stage of the Royal Oak Music Theatre: Lt. Gov. Brian Calley, Attorney General Bill Schuette and finally Gov. Rick Snyder, who introduced the man the crowd had come to see, Mitt Romney. Wearing jeans and a navy blazer, Romney spoke for about 12 minutes, giving a variation of his standard stump speech, quoting the lyrics of “America the Beautiful” and the Declaration of Independence.

“I happen to believe that if we want to have a strong economy and good private-sector jobs, it helps to have a president who’s had a private-sector job,” the former Massachusetts governor said, drawing cheers from more than 500 supporters in attendance in Royal Oak, a suburb of Detroit. Romney said his arguments for strengthening the economy are “the reason that I can defeat Barack Obama in Michigan in the fall.”

Before he can do that, of course, Romney must first show he can win Michigan in February and, on the eve of Tuesday’s GOP primary here, that proposition was still very much in doubt. While Romney has recovered from the slump that had him trailing by double digits in his native state two weeks ago, the latest polls show the longtime Republican frontrunner barely leading Rick Santorum. (One late poll even showed Santorum with a slight lead.) While Romney has outspent his Republican rival here and has deployed his professional campaign staff effectively, the intensity of the fight in Michigan has exceeded what anyone would have predicted a month ago. In 2008, Romney defeated John McCain here by an 80,000-vote margin, and Michigan was widely expected to be a “safe” state for Romney this time around.

Michigan isn’t safe because Santorum has appealed to the state’s blue-collar voters and religious conservatives, including his fellow Catholics who may account for as many as one-third of votes cast in Tuesday’s primary. In a Wall Street Journal op-ed column Monday, Santorum outlined his economic plan, which especially emphasizes the need to revive America’s manufacturing sector in industrial “Rust Belt” states like Michigan. Despite a widely criticized debate performance last week in Arizona, and despite a number of controversies that have generated national headlines, Santorum has stood up under the fire of Romney’s attack ads in Michigan in a way that Newt Gingrich was unable to do in Iowa or Florida. During a Monday appearance in Lansing, Santorum dismissed as a “joke” Romney’s ad campaign against him and told a crowd of about 200 supporters, “Michigan, you have an opportunity to stop that joke.”

On the eve of the primary, there was much talk of mischief in Michigan. Santorum’s campaign has repeatedly asserted that Romney and Texas Rep. Ron Paul have been strategically cooperating against him, a charge given credence by an analysis that found Paul had repeatedly attacked Romney’s rivals during debates, but never attacked Romney. Monday, the accusation of shenanigans was aimed at Santorum’s campaign, which used automated “robocalls” to target Democratic voters with anti-Romney messages. Michigan has an “open” primary law, meaning that independents and Democrats can vote in the Republican primary, and many Democrats have talked of crossing over to vote for Santorum, whom they consider an easier opponent for Obama than Romney.

Have the Democrats miscalculated? If the more moderate Romney is really a stronger candidate, why has he struggled to close the deal with voters of his own party here in his native Michigan? It hardly adds to Romney’s “electability” argument that — even with the backing of Michigan’s top Republican officials — he would consider himself fortunate to escape Tuesday with 40 percent of the vote and a narrow win over Santorum’s low-budget campaign. Even if Romney wins Michigan, one of Santorum’s top advisers told CNN Monday, “We have already won. No matter what the results are, we’ve won. This is Romney’s home state.… The Romney campaign is spending a fortune they never expected to spend in Michigan, and every dollar they spend in Michigan is a dollar they don’t have on Super Tuesday.”

The outcome of the primaries on Super Tuesday — a week from today, on March 6 — will likely be influenced by perceptions of today’s vote in Michigan. That is especially true of neighboring Ohio, where Santorum has already begun campaigning. But while it might be considered a symbolic victory for Santorum merely to come close to beating Romney in Michigan, an actual upset win for Santorum would be a major breakthrough for the 2012 campaign’s longtime underdog. Speaking to his supporters Monday in Lansing, Santorum made clear how high the stakes are.

“Tomorrow’s the big day. It could be a game-changing day,” Santorum told the audience, remarking that Michigan has in recent years tried to move its primary to earlier in the presidential campaign schedule. “Well, you’ve moved to the right place this time. You have a chance to be the inflection point in this race. Don’t miss the opportunity to stand up, and don’t pay attention to those who say, ‘Oh, we can’t elect someone who’s too conservative. We need to appeal to moderate voters.’ They said the same thing about Ronald Reagan. … It’s no wonder why all the Democrats and all the political experts are saying, ‘Oh, you can’t nominate Santorum, he’ll be a disaster. Ha ha ha.'” Santorum paused, then said, “He who laughs last, laughs best.”

Whether Santorum or Romney will be laughing Tuesday night is a decision that now rests, not with experts, pundits or pollsters, but with the voters of Michigan.