Ronald Reagan once famously admonished conservatives running for higher office not to attack each other in public. But with the political stakes growing in the 2012 GOP presidential race, don’t expect participants in tonight’s two-hour Republican presidential debate in New Hampshire to adhere to the so-called “Reagan rule.” In fact, tonight’s debate could well turn into a brawl.

Officially, tonight’s debate is the GOP’s second, but CNN, which is hosting the event live from 8-10 p.m. EST, is billing it as the first. And for good reason: It’s the first Republican debate to include former Massachusetts Gov. Mitt Romney, the presumptive GOP frontrunner, and Tea Party darling Rep. Michele Bachmann, the candidate who’s most likely to become — assuming that Sarah Palin doesn’t run — Romney’s chief antagonist among “movement” conservatives.

Romney, who enjoys a strong lead over other GOP candidates, not only nationally but in New Hampshire, is looking to tonight’s debate to consolidate his image as the most “electable” and “presidential” figure in the far-flung GOP field. A recent Washington Post poll found that Romney, alone among the current crop of GOP candidates, compares favorably with President Obama in a head-to-head contest for the White House.

But, of course, that doesn’t guarantee him the GOP nomination. And with polls showing that much of Romney’s support in New Hampshire and elsewhere is soft, there’s still time for someone else to emerge, despite Romney’s decided advantage in name recognition, funding and organization in most of the key primary states.

Bachmann, for example, is hoping to use her performance tonight to introduce herself to GOP voters, many of whom still know little about the Minnesota representative.

And judging from his past performances, former Godfather’s Pizza CEO Herman Cain, who’s already wowed Republican audiences with his blunt, no-nonsense pronouncements on taxes and regulation — and who many say “won” last month’s GOP debate in South Carolina — will likely claim his fair share of attention, too.

Like Romney, Cain has real private sector experience, and if tonight’s debate centers more on job creation than on health care or the deficit, as Romney clearly hopes, the former president of the National Restaurant Association, who earned an industry reputation for rescuing dying fast-food chains, could end up outshining Bachmann.

And don’t count out former Minnesota Gov. Tim Pawlenty, either. So far, he’s underperformed with GOP voters, but last week Pawlenty raised eyebrows among conservatives — and grabbed national headlines — by calling for reductions in federal spending far in excess of the most drastic GOP plans currently on the table. And he’s just launched a brand new publicity offensive on health care reform, suggesting that Romney’s approach and the president’s are virtually indistinguishable.

Also closely watched tonight will be Newt Gingrich, who’s apparently decided to soldier on despite the resignation of his entire paid campaign staff last week. Republicans have already taken Newt to the woodshed over his suggestion that Paul Ryan’s Medicare privatization plan amounted to “right-wing social engineering,” a remark for which Gingrich tried to apologize, without much success. Unencumbered by his political consultants, expect Newt to be Newt — only more so than usual.

It will be interesting to see how much of tonight’s debate focuses on foreign policy. Most of the GOP candidates have little foreign policy experience. Cain is likely to try to demonstrate some newfound knowledge of Afghanistan and the Middle East after embarrassing himself on these topics in national interviews in recent weeks. Bachmann, who, unbeknown to many, now has a seat on the House Select Committee on Intelligence, could also try to flaunt her credentials.

Part of the debate is likely to center on whether Republicans would cut the defense budget and limit foreign intervention, positions long held by libertarian Ron Paul and highly favored by the voters. Some prominent Tea Party groups also favor these positions, which could place Bachmann and Cain, who broadly favor a robust American foreign policy but who are critical of Obama’s recent Libya intervention, in a difficult position.

Expect Paul, though, to use much of his debate time to try to pull the other candidates his way on these issues, and to tie the party’s robust deficit reduction goals to a rethinking on foreign policy. Gingrich, though, could easily emerge as Paul’s chief antagonist, and could score big by positioning himself as a hawkish Reaganite. How Romney, in particular, positions himself in this discussion could prove to be revealing. Despite having traveled overseas in recent months, including to Israel, he’s been reticent to issue foreign policy statements, saying only that his business “negotiating skills” would be useful in diplomacy.

But to appear credible, Romney will have to say much more than that tonight.

Ironically, the GOP candidate with the most foreign policy experience — former two-term Utah Governor Jon Huntsman, who’s been an ambassador twice, most recently to China — is ducking the two-hour debate. After initially agreeing to participate, Huntsman withdrew to continue his whirlwind tour of rural New Hampshire, where’s he quietly introducing himself to Granite State voters, many of whom appear to be receiving him favorably, according to press reports.

Why did Huntsman drop out? Some observers question whether Huntsman is actually serious about running in 2012 and wonder if he’s just patiently laying the groundwork for a 2016 bid. Huntsman denies that, saying he’ll gladly participate in future candidate debates once he formally announces his bid.

Or maybe he’s just smart enough to know when the fireworks can get you singed.

Stewart J. Lawrence is a Washington, D.C.-based public policy analyst who writes frequently on immigration and Latino affairs. He is also founder and managing director of Puentes & Associates, Inc., a bilingual survey research and communications firm.