Nate Silver has updated his model:
PPP's final Michigan poll, which was released within the past hour, finds Santorum ahead:
Much has been made of Democratic efforts to turn out the vote for Santorum and we see evidence that's actually happening. Romney leads with actual Republican voters, 43-38. But Santorum's up 47-10 with Democratic voters, and even though they're only 8% of the likely electorate that's enough to put him over the top. The big question now is whether those folks will actually bother to show up and vote tomorrow.