Second, Santorum starts out in better shape in Michigan than in Arizona. A Rasmussen poll taken the first week of February showed Romney with a huge lead in Arizona, 48 percent to Gingrich’s 24 percent and Santorum’s 13 percent. At the same time, Rasmussen found Romney up in Michigan 38 percent to Gingrich’s 23 percent and Santorum’s 17 percent. Santorum is undoubtedly in better shape after his wins Tuesday. Still, he would rather start out in a state 21 points behind the leader than 35 points behind.

Third, Romney’s Michigan favorite-son advantage might not be decisive. “I don’t believe the home field advantage in Michigan is as strong as people think,” says pollster Scott Rasmussen. “In New Hampshire, Mitt Romney benefited from having been the governor of Massachusetts and having his face beamed into the state on a very regular basis. He had a home there. He was there all the time. Romney has roots in Michigan, but he does not have the same kind of presence he did in New Hampshire.”

Fourth, Michigan seems custom-made for Santorum’s message of reviving American manufacturing and paying more attention to the problems of American workers who don’t have college degrees. It’s something Santorum has been talking about since his earliest days of campaigning in Iowa, and it seems likely to resonate in Michigan.