Tomorrow night’s GOP debate in Arizona may be crucial in determining what the rest of the contest looks like. It could help decide when the eventual GOP nominee will be able to pivot to general election mode and how damaged he may be.

It’s the last debate before the crucial Arizona and Michigan primaries next Tuesday, and then Super Tuesday on March 6. It will probably be the last chance for anyone to really break through and seriously change what’s happening. So: What are each of the candidate’s goals?

Mitt Romney: He doesn’t want the debate to be the story. He wants to fight this campaign out in the arena of TV ads, where he holds a huge financial advantage. So his goal is to continue amplifying the message in the ads — hitting Santorum as being too “inside Washington” — while avoiding rocking the boat.

Also: Santorum has been landing effective punches on Romneycare; the Mittster needs to have a much better prepared comeback than he’s used so far.

Rick Santorum: He comes into the debate with a clear national polling lead, but having lost the momentum in Arizona and Michigan, where he’s being heavily outspent. The trick for him is twofold. He has to get away from contraception and other fringe social conservative issues (he has those votes locked up), and find an economic message that works for all conservatives.

At the same time, Santorum has spent most of the time at the debates trying to force his way into the conversation. Now that he’ll be center stage, it’s time for him to be a bit more presidential — and a bit more likeable.

Ron Paul: He has been attacking Santorum in ads. If he really wants to hit Santorum, the trick for him is to stick to spending issues where he’s to the right of the former Pennsylvania Senator — and to avoid foreign policy, civil liberties, and other issues where Santorum has successfully picked fights with Paul in previous debates, and which play well (in Republican primaries) for Santorum.

Newt Gingrich: He needs a Gingrich moment, such as an attack on the debate moderator that makes Republican voters squeal. His only chance to remain relevant is to win back votes in the South that are probably going to Santorum. If he doesn’t, he may drop out after Super Tuesday — giving Santorum a chance to consolidate conservative voters against Romney.

Debates never stand alone — these candidates are spending tons of money in the hotly contested states, and press coverage of the rest of the campaign matters a lot, too. But debates certainly have been important in this cycle, and I suspect we’ll have plenty of fireworks in Arizona.