This article is from the archive of our partner .

With just over one week to go before the big Michigan primary, new polls show Mitt Romney has closed the gap on Rick Santorum, but still has his work cut out for him in the Great Lakes State. Public Policy Polling's latest numbers say that in the last week Romney has turned a 15-point deficit into just four, which is now within the margin of error. But the polling also shows that the Romney is not making up ground at the expense of Santorum, whose favorably ratings and share of the vote have remained largely unchanged. Mitt has simply been winning over more and more of Michigan's undecideds. The poll also suggests that if Newt Gingrich were to drop out of the race, Santorum's advantage would grow once again.

One theory behind the surge is that Romney's overwhelming ad blitz may finally be sinking in. He's been blanketing the state with TV commercials for the last couple of weeks and doing his best to defend his anti-auto bailout pledge as a principled stand for conservatism — which is helped by the fact that less than 30% of those taking part in the latest poll are union members. Romney has big leads among women and moderates (suggesting the birth control dustup is not a winner for Santorum) and, oddly enough, among Catholics, despite the fact that his main opponent is one of them. (So is Newt Gingrich, however, so perhaps that's a divided vote problem.)

Five Thirty Eight also points out that the latest poll features a smaller percentage of evangelicals than PPP's previous effort, which could also explain at least part of the move towards Romney. That's likely to be the key block in next Tuesday's primary. If they come out for Santorum in big numbers, he should have no problem taking the state. Five Thirty Eight's Michigan projection still has Santorum winning, but it's going to be a long, tense week for both candidates.

If Rick does eke it out, then next Tuesday is looking to be a draw with Romney claiming Arizona, and the overall state count staying even. (Depending on who you believe in Iowa and Maine.) Looking ahead to some of the other upcoming races, Five Thirty Eight also has Santorum looking strong in both Ohio and Oklahoma, which are key Super Tuesday states. A University of Texas/Texas Tribune pools also gives Santorum a huge edge in Texas, which has a ton of delegates up for grabs, but may have to delay its vote due to a redistricting fight. Either way, it seems clear that Santorum is in this race for the long haul and convincing more and more voters that he's a legit contender for November. Or worse from the GOP perspective, that Romney isn't.

The big movement in Michigan shows that when Romney presses his money/advertising advantage, he can make up a lot of ground. The problem is that he's constantly playing from behind. He's had almost a full month of laser-like focus on Michigan, but after the February 28 vote comes Super Tuesday. Then the primary votes will come much quicker, shortening the time he has to make up those big gaps. And with rumors that Romney's big donors are tapped out when it comes to donations, his biggest strength quickly becomes a glaring weakness.

This article is from the archive of our partner The Wire.

We want to hear what you think about this article. Submit a letter to the editor or write to letters@theatlantic.com.