Heading into Tuesday's Alabama primary, a PPP survey shows Mitt Romney narrowly leading with 31 percent, followed by Newt Gingrich (30 percent), and Rick Santorum (29 percent).

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"Tuesday's Republican primaries in Alabama and Mississippi may be the most suspenseful so far," says Mark Blumenthal at The Huffington Post. Polls shows "a three-way dead heat" in Alabama between Mitt Romney, Rick Santorum, and Newt Gingrich, with Romney and Gingrich essentially tied in Mississippi. Here, a look at four potential outcomes of Tuesday's races, and what they might mean for the GOP presidential race:

1. If Gingrich wins both races, Santorum is in trouble
After pinning his hopes on a "Southern strategy," Newt really needs to win Mississippi and Alabama to prove he's a contender in the GOP race. And remember, says Robert Costa at National Review, "Gingrich's challenge is not only to beat Romney, but also to halt Santorum's rise," since both the not-Romneys want a clear one-on-one race with the frontrunner. Indeed, "if Santorum loses to Gingrich on Tuesday," says Paul Steinhauser at CNN, it undercuts his main argument for staying in the race: "That he's the conservative alternative to Romney."

2. If Santorum wins both races, it's the end of Gingrich
Unlike Gingrich, Santorum doesn't necessarily have to win both states to remain a viable candidate. But he really wants to, says CNN's Candy Crowley. Team Santorum is hoping a pair of Tuesday victories will "blow up the Gingrich campaign's Southern strategy and muscle Newt out of the race." Winning in the heart of the Deep South would also build on Santorum's victories last week in Tennessee and Oklahoma, showing he has appeal outside of Midwestern caucuses.

3. If Santorum and Gingrich each take a state, Romney wins
"Romney's preferred scenario, as time drags on and the November election draws nearer, is to get this nomination over with already," says Michael Crowley at TIME. But his second-best option is for both Gingrich and Santorum to stay in the race, splitting the conservative vote while Mitt quietly racks up enough delegates to win the nomination. "The scenario that most people are discussing right now — the possible departure of Newt Gingrich, if he bombs in Tuesday's Southern primaries — is the one Romney should fear most." Mitt would surely rather see his conservative rivals each win a race on Tuesday, ensuring that the Right won't unite behind a single non-Romney candidate.

4. If Romney wins either race, it's game over
"Romney has a shot to win both states," says Jonathan Martin at Politico, and wouldn't it be a fitting end to the "topsy-turvy GOP primary" if "the Mormon Yankee who thinks cheese grits are a revelation effectively seals the nomination in Alabama and Mississippi"? Yes, if Romney "adds a win in either Alabama or Mississippi," GOP strategist Gentry Collins tells CNN, that's enough to "shut his opponents' Southern strategy down." The best part for Romney is that nobody really expects him to win, says Chris Cillizza at The Washington Post. So a victory in either state would be "an expectations-altering sort of win," washing away doubts about his candidacy "for the moment if not forever."