Byron York

Thursday, Feb. 9 was just the second time Rick Santorum's campaign has raised more than a million dollars in a single day. The first was the day before, immediately after Santorum swept GOP contests in Minnesota, Colorado and Missouri. That's what winning will do. Santorum is now enjoying the bounce he never got after his belated victory in Iowa. The question is, what is he going to do with it?

The next primaries are on Feb. 28 in Arizona and Michigan. They're both big, they're both important, and they're both states in which Mitt Romney will have some advantage. Arizona has a significant Mormon population -- less than Nevada, where Romney won with 90-plus percent of the Mormon vote, but still significant. Michigan is where Romney was born and raised and where his father served as governor.

Add to that Romney's advantages in money and organization, and Santorum has an uphill climb. And then, after Arizona and Michigan, come the March 6 Super Tuesday contests. So even with those million-dollar days, Santorum will have to pick and choose which states to target.

In the short run, it appears he's looking closely at Michigan, for several reasons. First, while Romney won the state solidly in 2008, it wasn't a blowout: 39 percent for Romney to John McCain's 30 percent and Mike Huckabee's 16 percent. (Ron Paul, Fred Thompson and Rudy Giuliani won a combined 13 percent.) No one can say Romney has a lock on Michigan.

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 recent wins. 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."

Byron York

Byron York, chief political correspondent for The Washington Examiner