Marquette, Mich. ? The question of whether Mitt Romney is conservative enough to deserve the Republican presidential nomination regained center stage in the GOP contest Sunday, with Rick Santorum saying the former Massachusetts governor fails the test.

Santorum urged Michigan voters to turn the race “on its ear” by rejecting Romney in Tuesday’s primary in his native state, in which Romney is spending heavily to avoid an upset. Santorum said Romney’s record is virtually identical to President Barack Obama’s on some key issues, especially mandated health coverage, making him a weak potential nominee.

“Why would we give away the most salient issue in this election?” an impassioned Santorum asked more than 100 people in a remote, snow-covered region of Michigan’s Upper Peninsula. Santorum, a former senator from Pennsylvania, said he is the true conservative on fiscal and social issues.

Romney rejected the claims.

“The biggest misconception would be that I’m a guy that comes from Massachusetts and therefore I can’t be conservative,” Romney told “Fox News Sunday.” In his one term as Massachusetts governor, he said, he balanced budgets, reduced taxes, enforced immigration laws, “stood up for traditional marriage” and was “a pro-life governor.”

“I’m a solid conservative,” Romney said.

The exchanges highlighted the choice facing Republican voters in Arizona and Michigan on Tuesday and another 10 states a week after that.

Campaigning later in Traverse City, Romney emphasized his Michigan roots and made clear to the crowd just how important a victory is in the state, where he was born and raised. “On Tuesday, I need a big voice coming from right here,” he said.

Romney did pick up the endorsement of Arizona Gov. Jan Brewer on Sunday.

He also took a detour to the Daytona 500 in Florida, where he talked with fans. Asked by The Associated Press if he follows the sport, Romney said, “Not as closely as some of the most ardent fans, but I have some great friends that are NASCAR team owners.”