Heavyweight contenders for the Republican presidential nomination will join long-shot candidates Monday night in New Hampshire in what feels like the first real debate of the 2012 cycle. 

A fuller cast of Republicans will be onstage Monday night at 8 p.m. in Manchester for the two-hour debate, broadcast on CNN — more than compared to the early-May debate in South Carolina, which some front-runners skipped.

Former Massachusetts Gov. Mitt Romney, former Minnesota Gov. Tim Pawlenty, former House Speaker Newt Gingrich (Ga.), Rep. Michele BachmannMichele Marie BachmannYes, condemn Roseanne, but ignoring others is true hypocrisy Bachmann won't run for Franken's Senate seat because she did not hear a 'call from God' Billboard from ‘God’ tells Michele Bachmann not to run for Senate MORE (Minn.), Rep. Ron Paul (Texas), former Sen. Rick Santorum (Pa.) and businessman Herman Cain round out the cast of Republicans set to appear at St. Anselm College.

And while several potential candidates — including former Alaska Gov. Sarah Palin, former Ambassador to China Jon Huntsman, New York City Mayor Rudy Giuliani and Texas Gov. Rick Perry — won't be onstage, the debate will offer clues as to how the race for the 2012 Republican nomination has shaped up.

Here are five things to watch for:

Romney vs. Pawlenty

The headlining aspect of this debate may well be the showdown between Romney and Pawlenty, two of the leading contenders for the nomination, who will share the stage for the first time as presidential candidates.

While the former Minnesota governor had, to date, declined to level much criticism at Romney's Massachusetts healthcare law, that changed Sunday, when Pawlenty coined the term "ObamneyCare" as an epithet to politically tether the president's and Romney's plans together.

"President Obama said that he designed ObamaCare after RomneyCare and basically made it ObamneyCare,'" Pawlenty said on "Fox News Sunday." "The president's own words is that he patterned in large measure ObamaCare after what happened in Massachusetts. And what I don't understand is they both continue to defend it."

One of Romney's top advisers fired back Sunday afternoon on Twitter, but observers will be watching for Romney's response Monday night. 

Romney offered his explanation for the law last month during a speech in Ann Arbor, Mich., but the debate will be a crucial test of how well his defense will hold up to scrutiny with primary voters.

Will Gingrich rebound?

Beyond Romney and Pawlenty, the most closely watched single candidate could be Gingrich, who is trying to rebound from a political meltdown last week that resulted in the mass resignation of most of his top campaign aides.

Both the departed aides and Gingrich acknowledged that the resignations were the product of a disagreement over how to manage the former Speaker's campaign. Now Gingrich will have to offer a well-crafted explanation at the debate as to why voters shouldn't leave his campaign for dead and look at other candidates in the race.

Part of Gingrich's challenge will be demonstrating that he has the focus to be an effective candidate and get his campaign back on track. That's important not only to rank-and-file Republican voters, but also to the GOP's elite class, particularly deep-pocketed donors, who could provide Gingrich with a fundraising boost his campaign badly needs.

Whether other candidates seize on Gingrich's political misfortune is an open question; they have mostly avoided direct criticism of the former Speaker and his previous gaffes, but the debate provides an opportunity.

Who isn't there?

Some of the biggest players in Monday night's debate will be the candidates who aren't even onstage in Manchester.

Palin, one of the campaign's biggest X-factors, won't be at the debate. But the specter of her potential candidacy looms large, both in terms of questions the other debate participants face, as well as how the candidates position themselves to attract (or avoid) Palin supporters in her absence.

Former Ambassador to China Jon Huntsman (R), who could be only days away from entering the race, also won't be participating in the debate, despite New Hampshire's central role to his campaign. In many ways, Huntsman's likely base of voters in the state overlaps with Romney's, and the former Utah governor might be content to sit back and and let some of the other Republicans in the race take down Romney a few notches for him.

Moreover, both Perry and Giuliani won't be at the debate, though if either chooses to enter the race, it could redirect the trajectory of the campaign. Former New Mexico Gov. Gary Johnson, a libertarian-leaning Republican, has also been denied a chance to appear at the debate.

How will Democrats react?

Democrats will be closely watching the debate for signs of vulnerability in each candidate, which they'll happily exploit as the campaign unfolds.

A variety of liberal groups will join the Democratic National Committee (DNC) and the New Hampshire Democratic Party in crafting "prebuttal" events today in the Granite State, and generating pushback during the debate itself.

"Monday's Republican presidential debate in New Hampshire isn't the first of the 2012 election, but it may be the first one that counts," the DNC's communications director, Brad Woodhouse, wrote to supporters in an email promising real-time fact checking and spin during the debate. "This time, they're bringing their varsity squad: Mitt Romney and Tim Pawlenty will be there, along with Herman Cain (polling second in Iowa), Ron Paul, Newt Gingrich, Michele Bachmann and Rick Santorum."

The president himself will be at campaign events early Monday evening in Miami, where he'll deliver remarks at a pair of DNC fundraisers shortly before the debate. It's unclear whether Obama intends to watch the debate.

And Protect Your Care, a liberal group dedicated to defending Obama's healthcare law, is gleefully meddling in the race by launching TV ads and damning Romney's health law on the right with its praise.

Shades of Tea

While some of the candidates make their pitch to the whole GOP electorate, watch out to see which candidates try to seize the mantle of the ascendant Tea Party.

Bachmann founded the House Tea Party Caucus and is seen as a figure with fairly close ties to the activist conservative movement. But Paul, the libertarian Texas congressman who attracted a dedicated following during his 2008 campaign for president, is seen as something of a godfather of the movement; his son, Sen. Rand PaulRandal (Rand) Howard PaulSenate passes 6B defense bill This week: House GOP caught in immigration limbo Amendments fuel resentments within Senate GOP MORE (R-Ky.), is also popular with grassroots conservatives. 

Cain has also won some Tea Party support and enjoyed a bump in support in some polls, and even Pawlenty's made his own pitch to the Tea Party.