Manchester, N.H. — The GOP primary debate – the first one this election cycle to include heavy hitters Mitt Romney, Newt Gingrich, and Michele Bachmann — will begin in about an hour. For all the candidates, the debate’s a chance to win over some voters — or alienate some. They also have their own individual challenges.

Watch for Romney to face questions about Romneycare, and most likely, some jabs from other GOP candidates. (Tim Pawlenty already came out swinging yesterday morning, talking about ‘ObamneyCare.’) And as frontrunner, he’s under significant pressure to turn in a commanding performance.

Gingrich, who lost the majority of his senior staff in a mass resignation last week, has to establish he’s still a viable candidate. Known for his debating skills, Gingrich could begin to reverse the narrative that he’s a floundering candidate by bowling over his opponents today.

Pawlenty, who’s enjoyed a rash of good publicity in recent days, thanks to his new focus on economic growth by pushing for tax and spending cuts, could build on that momentum tonight. With Jon Huntsman and Gary Johnson both absent from tonight’s debate stage, Pawlenty will be the only other governor besides Romney — which allows him to further make the case he’s the candidate for those who appreciate Romney’s executive experience, but are looking for another candidate.

For Ron Paul, tonight’s another chance to make the case that he’s a candidate able to win over enough voters to triumph in a primary, not limited to his core base of libertarian supporters. Rick Santorum, who’s been dogged by low poll numbers, emerged as the sharpest critic in the last debate. Don’t be surprised if he tries to stand out from the pack with the same tactic tonight.

Bachmann, the only person on stage tonight who hasn’t officially declared, can burnish her tea party credentials tonight — and prove (or not) that she has the chops to handle the national stage. Herman Cain, who wowed audiences with his debate performance in May, could do the same tonight, shooting ahead of his more politically-experienced opponents with his trademark mix of charm and common sense talk.

Tonight likely won’t be a game-changer. But in this competitive, crowded field, any performance that gains (or costs) a candidate a few points in the poll could mark an important shift.

(Photos courtesy of CNN)