A new Public Policy Polling survey shows that Rick Santorum trails Mitt Romney by only 3 percentage points among Arizona Republicans, who will decide the state's primary election on Feb. 28.

Romney has the support of the 36 percent of Arizona Republicans, while 33 percent support Santorum.

This is the third poll in the last week to show a tightening race between Romney and Santorum in Arizona. Previous surveys by Rasmussen and American Research Group have Santorum surging in the Grand Canyon State.

The PPP survey drills down into where the support for Santorum and Romney—as well as other candidates—is coming from. It notes that Romney is losing the Tea Party vote; Santorum is better liked by Arizona Republicans than Romney; and an endorsement from Maricopa County Sheriff Joe Arpaio or Gov. Jan Brewer could be a game-changer.

It also notes that Congressman Jeff Flake is clobbering GOP challenger Will Cardon.

The analysis:

The Republican race for President in Arizona looks like a close one, with Mitt Romney leading Rick Santorum only 36-33. Newt Gingrich is third at 16% and Ron Paul fourth at 9%.

Santorum is better liked by Arizona Republicans than Romney, but the gap isn't as wide as we're finding in a lot of other states. Santorum's at +34 (61/27), while Romney's at +24 (58/34).

One thing to keep an eye on over the next week is whether Newt Gingrich can hold his support. 16% is pretty good for him compared to what we're finding other places right now, but only 46% of his voters say they're solidly committed to him. 40% of his supporters say that Santorum is their second choice, compared to only 25% for Romney. If Gingrich's supporters see he's not viable and decide to jump ship the race could get even closer.

Santorum and Romney are both generally winning the same groups we find them winning in Michigan and nationally right now. The reason Romney's leading in Arizona but trailing in those other places is that he's at least staying competitive with the groups he tends to be weaker with. For instance he's only down by 11 points with Tea Party voters, 43-32. He's only down 13 with those describing themselves as 'very conservative,' 44-31. And he's down just 18 with Evangelicals, 45-27. Those are all groups he's losing by more than 25 points in Michigan right now.

Romney's up by good sized margins in Arizona with seniors (41-32), Hispanics (41-30), women (39-31), 'somewhat conservative' voters (43-29), and moderates (39-22). It's kind of a given at this point that Romney will take moderates and Santorum 'very conservative' voters. The 'somewhat conservative' ones are really the swing voters of the GOP electorate and they're leaning towards Romney in both Arizona and Michigan right now.

John McCain's endorsement isn't doing Romney a whole lot of good in Arizona. Only 15% of voters say they're more likely to vote for a McCain endorsed candidate, compared to 30% who consider it a negative, and 53% who say it doesn't make a difference either way.

There are two endorsements that could have a bigger impact in the final week of the campaign. 32% of voters would be more likely to support a Joe Arpaio endorsed candidate, compared to 24% who would be less likely to. And 25% would be more likely to support a Jan Brewer endorsed candidate, compared to 21% who would be less likely to. If Romney or Santorum could nab either of those endorsements it would be a boost.

Like in Michigan this is still an extremely volatile race, with 44% of voters open to changing their minds between now and the election. GOP voters if anything are becoming even more indecisive as this contest wears on. Romney's supporters are a little more committed with 60% saying they'll definitely vote for him compared to 56% of Santorum's voters who say that.

The Republican Senate race in Arizona doesn't look like it will be much of a race. Jeff Flake's at 56% to 7% for Wil Cardon, 5% for Bryan Hackbarth, 1% each for Douglas McKee and Clair Van Steenwyk, and 0% for John Lyon.