• Edward M. Pio Roda/CNN

It appears that Rick Santorum's weak debate performance last week was a game-changer for him—in the wrong direction. Public Policy Polling's latest numbers have Mitt Romney crushing Rick Santorum:

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.

Santorum's image has taken a big hit over the last week in the state. His net favorability has dropped 15 points from +34 (61/27) to just +19 (54/35). The debate Wednesday night may have damaged his cause. 51% of likely voters report having watched it and he's actually in 3rd place with those folks at 21%, behind Romney's 43% and Gingrich's 23%.

Santorum may also have misstepped by talking too much about social issues in the last few weeks. 68% of Arizona voters say economic issues are their top concern when deciding who to vote for, compared to just 11% who say social issues are paramount. With the folks most concerned about economic issues he trails Romney 48-24.

It's worth noting that Romney's improved his image in the closing stretch in Arizona- it's not just bringing down Santorum that's put him in position for this big win. Romney's net favorability is now +31 at 62/31, up from +24 at 58/34 a week ago.

We had been planning to do a 2 night Arizona tracking poll but with the numbers this lopsided we're not going to bother, so this will be our final word on the race there.