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Polls show Mr. Romney leading in Arizona and running neck-and-neck with Mr. Santorum in Michigan, where the former venture capitalist also has said he believes that General Motors and Chrysler should have entered into a managed bankruptcy process instead of taking the federal bailout.

Many political observers say that if Mr. Romney wants to win the nomination, he likely has to win in Michigan, where he grew up and his father served as both an automobile executive and governor. The former Massachusetts governor has the support of the state’s current governor and the attorney general, as well as the endorsement of the Detroit News.

But Mr. McKenna said Mr. Santorum’s message is making him competitive.

“He understands what people ultimately care about is not policies, it is philosophies, and that is something Romney never understood and it is something that George Bush never understood. You are not buying a set of policies. You are buying a philosophy and hoping they can apply that to the problems of the day,” he said.