“His family made a substantial effect on our state, and you just can’t take that away from him,” said Al Heilman, 76, who said he still had a photograph socked away somewhere of himself meeting Mr. Romney’s father decades ago.

Mr. Heilman, a Republican chairman from Kalamazoo County in the southwestern part of the state, said some people seem to want to penalize Mr. Romney for his business experience. “I don’t understand people who kick people in the shins because they’ve been successful — profits make the world go around,” Mr. Heilman, who retired after running a confections and nuts business, said. “Look, we’re on a dive, and this is the time for a true businessman like Mitt Romney who can turn around the country.”

In places like Oakland County, the suburbs outside Detroit where Mr. Romney was raised, he is expected to make some of his strongest showings. Among hundreds of well-dressed Republicans who strolled into a Lincoln Day dinner in a ballroom here in Novi the other night, many referred to their choice for president simply as “Mitt,” and a few actually said, “Who else?”

But even here there also are shaky signs. Frank Spatafore, 74 and a retired industrial engineer, said he was stunned when his small club of Republican friends polled its presidential preferences at a recent meeting, and Mr. Santorum won.

“I know that Mitt Romney is a good guy and a good family man, but when a politician form-fits himself so much to what he thinks people want, I just don’t know anymore,” said Mr. Spatafore, who added that he, too, favored Mr. Santorum.

In this part of the state, where nearly everyone knows someone who has worked in the car business, Mr. Romney’s comments about a federal bailout for American automakers have drawn special notice. Mr. Romney has said he believes that General Motors and Chrysler should have entered into a managed bankruptcy process without an infusion of federal assistance. His position puts him in a slightly uncomfortable spot, even beside some who have endorsed him, like Gov. Rick Snyder, who has taken care not to criticize the auto bailout.

But Mr. Romney’s opposition to a bailout is more far more likely to be an issue in a general election here — where Democrats have won presidential elections since 1992 — than in a Republican primary. For one thing, Mr. Santorum, too, has spoken against the bailout. Perhaps more importantly, some Republican voters — even those who excitedly described how Michigan’s auto industry now appears to be returning, with growing jobs and record profits — say that they, too, oppose government bailouts, even for Michigan’s beloved cars.