Could Rick Santorum topple Mitt Romney in Arizona?

While polls in recent weeks have suggested that Mitt Romney is vulnerable to Rick Santorum in his home state of Michigan, he has always counted on winning at least one state in next week's primaries: Arizona.

It's a Western state with a sizeable Mormon population; its Republicans are less socially conservative and more Libertarian than in some Midwest states where Santorum does well; and Mr. Romney has been well ahead in all polls there.

But a new poll from CNN/Time Tuesday suggests that Mr. Santorum may be closing the gap in Arizona as well.

The poll has Romney with 36 percent of likely primary voters, compared with Santorum at 32 percent. Newt Gingrich has 18 percent, Ron Paul has 6 percent, and 6 percent are undecided. The 4 percent difference between Romney and Santorum is within the poll's margin of error – meaning they're essentially tied.

The poll comes on the eve of Wednesday's debate in Mesa, Ariz. -– the last GOP debate before next Tuesday's primaries and the following week's Super Tuesday events.

And it will be a critical debate for both Romney and Santorum. According to the CNN poll, about one-third of voters are still open to changing their mind in the next week.

Next week's contests will also be the first chance to see if Santorum can win in a primary election, rather than a caucus. The major states he's won so far have all been caucus states – which tend to emphasize the favorite candidate of more extreme, impassioned voters. These contests have been tough on Romney, who inspires less enthusiasm even among his supporters.

An Arizona win would be especially helpful for Santorum, since it would be in territory presumed to favor Romney, and his first win outside of the Midwest, the region where he seems most at home. Even a very close second-place showing might be good for him.

According to the CNN/Time poll, the electoral divisions in Arizona mirror those in many other states. Santorum has the edge among evangelical Republicans and tea party supporters; Romney beats him by a sizeable margin among non-evangelicals and Republicans who don't favor the tea party. Romney also leads in urban areas, but not in suburban and rural areas.

"Class and gender may also play a role on February 28, with Romney doing best among Republican women and among GOPers who describe themselves as white collar," says CNN polling director Keating Holland.

The poll is hardly definitive. A week is a long time in this exceptionally volatile nominating season, when candidates' popularity seems to peak and plummet from day to day. Polls up until now have given Romney a sizeable edge in Arizona. (The Real Clear Politics rolling average has Romney up by about six points in the state.)

Still, the momentum right now seems to be going Santorum's direction – and the fact that Arizona is even in play is not good news for Romney.

All of which makes Wednesday night's debate even more interesting.

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