The Big Questions: By Mark Halperin

Is the Republican presidential race simply a Mitt Romney vs. Rick Perry battle?

By many measures, the GOP fight does look like a one-on-one affair. Romney and Perry lead in polling, fundraising, insider backing and media attention. But both are pockmarked with flaws. Questions remain about Romney’s people skills, not to mention the conservative anger over his Massachusetts health care law. Perry’s debate chops have been panned, while his overrelying on his Texas record has made him appear provincial. These vulnerabilities help explain Herman Cain’s Florida straw-poll win.

What about additional candidates?

The political world is on fire with talk that New Jersey Governor Chris Christie might run. He would almost certainly open strong; the question is whether he could survive a late start and a lack of preparation. Meanwhile, the clock ticks down on Sarah Palin’s already protracted decision. Having squandered much of her political juice, she would not arrive with top-tier potency. But in an unpredictable year with no dominant front runner, it’s nuts to rule anything out, especially before television ads (particularly negative ones) enter the equation, as they will soon.

Could anyone else overtake the two front runners?

Godfather’s Pizza honcho Cain rode his appeal as a straight-talking, personable outsider to his Sunshine State stunner. But the same private-sector-only résumé that excites his supporters also limits his chances to steal a state. The real danger to Romney and Perry lies elsewhere: Rick Santorum, who has tangled well with both men in debates, could soar in Iowa, where Perry has staked his claim. Jon Huntsman is showing signs of life in New Hampshire, where Romney expects to win. A surprise in either state could throw the race into turmoil.