Rick Santorum has risen to the top of the Republican polls in Michigan, according to Public Policy Polling. While PPP notes that Santorum's support isn't as strong as Romney's, it's still a very bad sign for the Romney campaign, which counted on the continued Republican popularity of Mitt's dad (and former Michigan Governor) George Romney as a solid base of support.

Meanwhile, the National Review is calling for Newt Gingrich to drop out so Santorum can make a clean run at Romney. I expect a lot of Republicans to join the National Review this week in calling for Gingrich to suspend his campaign; I don't see another sudden burst in the polls anywhere in his near future.