Which leads one to wonder if Santorum has ridden a temporary pivot of voter interest to Obama's controversial mandate.

"He's dropped back a little bit in the polls the last couple days because of the ads that Romney's playing now," said Dennis Pittman, Oakland County GOP executive director. "Santorum's being characterized for his 16 years as a representative and a senator raising taxes multiple times, raising the debt ceiling multiple times -- if you spend 16 years in Congress you're going to take some votes that are going to come back to haunt you, and Romney's being very effective at making sure everybody knows what his record is."

Indeed, since the weekend Santorum and Romney have fallen within the margin of error in most of the major Michigan polls.

Romney's campaign launched a two-pronged effort against Obama and his Republican opponents when he announced the new tax proposal. First, Obama unveiled his own tax proposal on the same day, which Romney saw as an opportunity to be the single Republican with a contrasting option. Second, he went back to economic fundamentals in an effort to shift the focus to employment and voters' bank accounts during difficult times.

Though many Republican Party officials in Michigan acknowledge Santorum is winning the state, despite a thinner ground presence, they also point out that there's a whole week for Romney to scramble back to the top.

"My observation is that it's a Romney-type electorate and in talking with the people ... is that he will probably succeed in getting Michigan," said Al Heilman, Kalamazoo County GOP chairman. "Remember what happened with each of the other candidates , they all came to the top and then they all went by the wayside; so we're back to two people and Rick is up there very strongly, but on the other hand the last 72 hours makes a difference.

Michigan voters, according to Michigan Republican Party officials, are concerned about beating Obama and about jobs and the economy, but another reason Santorum spiked and Romney lulled could be as basic as how familiar state voters are with the candidates.

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