For a while after Rick Santorum’s sweep in early February, it appeared that Mitt Romney might be on the ropes in the Republican primary.  Santorum once held a significant lead in Michigan and close to a tie in Arizona, and seemed poised for another multi-state upset.  According to the latest polling from PPP in both states, though, the momentum has swung in the other direction.  In PPP’s poll of Michigan, Romney has begun to edge Santorum one day ahead of their primary, but also with a significant lead in early voting:

Mitt Romney’s taken a small lead over Rick Santorum in PPP’s newest Michigan poll. He’s at 39% to 37% for Santorum, 13% for Ron Paul, and 9% for Newt Gingrich. Compared to a week ago Romney’s gained 6 points, while Santorum’s just stayed in place.

Romney will go into election day with a large lead in the bank. Only 16% of Michigan voters say they’ve already cast their ballots, but Romney has a whooping 62-29 advantage over Santorum with that group. Santorum actually leads Romney 39-34 with those who are planning to cast their votes on Tuesday, but he’d need to win election day voters by even more than that to neutralize the advantage Romney’s built up.

The last week of the campaign in Michigan has seen significant damage to Santorum’s image with GOP voters in the state. His net favorability has declined 29 points from +44 (67/23) to now only +15 (54/39). Negative attacks on Romney meanwhile have had no negative effect with his favorability steady at +20 (57/37). Two weeks ago Santorum’s net favorability in Michigan was 34 points better than Romney’s. Now Romney’s is 5 points better than Santorum’s. Those kinds of wild swings are the story of the GOP race.

One place Santorum may have hurt himself in the last week is an overemphasis on social issues. 69% of voters say they’re generally more concerned with economic issues this year to only 17% who pick social issues. And with the overwhelming majority of voters more concerned about the economy, Romney leads Santorum 45-30. Santorum’s winning those more concerned about social issues 79-12 but it’s just not that big a piece of the pie.

The debate did Santorum no favors in Michigan, although it may have been the aftermath of the debate that did more damage. Instead of focusing on a positive message, Santorum felt the need to go after Romney hard — much like Newt Gingrich did in Florida.  Santorum got his surge by sticking to blue-collar economics and directing his passionate attacks against Barack Obama rather than his Republican competitors; it appears that the mediocre debate performance knocked Santorum off of his previously-successful strategy.

The sample in this case looks pretty solid.  The D/R/I in the sample for Michigan’s open primary is 5/67/28 — a near duplicate of the exit poll from Michigan’s 2008 primary of 7/68/25.  Forty-two percent identified themselves as evangelical Christians, which seems high against the 2008 exit polling, which didn’t ask the question the same way but had 40% Protestants, 29% Catholics, and 19% “other Christians.”  Whatever problems Santorum has in this poll, they’re not related to the sampling.

Arizona would have been a long shot for Santorum under any circumstances, and PPP’s new poll makes it clear that Romney will get an easy ride in the winner-take-all state:

Mitt Romney is headed for an overwhelming victory in Arizona’s primary on Tuesday. He’s at 43% to 26% for Rick Santorum, 18% for Newt Gingrich, and 11% for Ron Paul.

You can make a fair argument that Romney’s already won the Arizona primary. Almost half of those planning to vote have already cast their ballots, and Romney has a 48-25 advantage over Santorum with those folks. That lead makes it nearly impossible for Santorum to make up the difference on election day, and Romney has a 39-27 advantage with those planning to vote on Tuesday anyway.

Romney’s winning basically winning every voter group in Arizona, even those he’s tended to do quite poorly with. He leads Santorum 39-33 with Evangelicals, 39-23 with Tea Party voters (Santorum’s in 3rd, Gingrich is actually 2nd at 30%), and 37-29 with those describing themselves as ‘very conservative.’ We project the Mormon vote at 14%. Romney leads 77-9 with them, but he has a 38-29 advantage with non-Mormons as well. Seniors are a key base of support for him in Arizona as they are everywhere. He leads 53-22 with them.

ARG has it much closer in Arizona at 39/35 Romney in a poll taken Thursday and Friday.  However, they also show a big advantage for Romney among early voters, 50/29, and 48% of their sample had already cast their ballots.

A loss in Arizona won’t matter as much to Santorum as a loss in Michigan will.  A loss in a key Rust Belt state, where Santorum’s draw among blue-collar workers should be felt most, will be seen as a setback after his large polling leads of a week ago.  Santorum needs the momentum from at least one win to help him sail through a tough Super Tuesday next week.  We’ll see what other pollsters say about Michigan today, but with Rasmussen also seeing a Santorum slide to second (by six points rather than two), the PPP poll doesn’t look like an outlier.