While polls show Mitt Romney heading to an easy victory in Arizona, polls in Michigan — where Romney was pulling into the lead late last week — are very, very close, and while it might be a statistical blip, there’s some indication that Rick Santorum’s numbers have been improving late in the race. Based on yesterday’s polling, PPP says that if Romney loses, “there’s not much doubt he will have blown it in the final 48 hours.”

The stakes today are fairly high for both candidates. If Romney can’t pull it out in Michigan, where he won in 2008 and where his father was once governor, it’s hard to see him winning the kind of near-sweep on Super Tuesday next week that would restore the air of inevitability that keeps not-quite-sticking to his campaign. If Santorum wins Michigan, it will begin to seem possible that he might snag the nomination out from under Romney (not least because a Santorum win today would almost certainly precipitate a significant fundraising bounce). Conversely, if Santorum can’t win today, his sweep of the February 7th contests begins to look less like a sign of a campaign with real staying power and more like a blip (which is about what Newt Gingrich’s South Carolina victory looks like at the moment).

Polls close at 8 pm local time tonight; that’s EST for most of Michigan, CST for four counties in the western Upper Pennisula.