Last night the four remaining Republican candidates took part in the final debate ahead of the primary for the battleground state of Florida on 31 January. There was a degree of role reversal in the performances; frontrunners Newt Gingrich and Mitt Romney repeatedly pressed, ridiculed and challenged one another -- the former showing less fight and momentum than his polling figures have suggested in recent weeks.

The verdict has largely fallen on the side of Romney as victor; though the other two candidates, Rick Santorum and Ron Paul, held the spotlight and audience applause in surprisingly large measure at this late stage in the race for nomination.

Here's the main five things, and corresponding clips, that we learnt from last night's crucial debate for the final four GOP candidates:

1) Romney's got bite

Early in the debate, Mitt Romney shamed rival Newt Gingrich over his claim the former Governor of Massachusetts was the "most anti-immigrant candidate." Romney called Gingrich's words "absolutely inexcusable" and "repulsive", while to his right the former House Speaker stood around uncomfortably. The crowd were behind Romney, and continued so whilst he stared Gingrich straight in the face, awaiting an apology.

2) Paul's king of the one-liner

He's going to hold on and keep them laughing until the bitter end. Conveying policy seemed not to be at the top of Ron Paul's agenda last night, but he certainly pleased the crowd.

The Texas congressman is not actually running in the Florida primary, but as in previous years, his safe base of supporters (and his health) will see him through the Presidential nominee race until he is finally forced out.

3) Gingrich shows signs of wearing down

After the immigration scuff, Romney continued to fire accusation of inadequecy at Gingrich, who responded to the attacks with weak anecdotes and complaints. The crowd were unimpressed.

Over in the Marbury blog, this was Ian Leslie take on Gingrich's performance:

[Gingrich was] tetchy, overly defensive and tired. He allowed Romney, whom he clearly despises, to get under his skin. He was too easily goaded into rhapsodising about space programs, which, even in Florida (home of the Space Coast), can make him seem a little detached from reality.

4) American's don't fear China "dominating space"

During the debate Gingrich was given the opportunity to expand on his proposals to build a moon colony -- for the benefit of the US economy -- were he to become president. In response, Romney relished saying he would fire Gingrich for such an idea, were he his boss, and swiftly moved on to attacking his rival's record of making state-specific pledges, vacuously "promising billions and billions of dollars to make people happy".

5) Santorum is hardly running, but he probably won

He is coming last in the polls and the pockets of his campaign may be empty, but Rick Santorum made an impressive performance on stage. He emerged the most successful candidate in holding Romney to account on policy; in many ways playing the part that Gingrich failed to claim. The former Senator for Pennsylvania spoke passionately "about freedom" in an attack on Romney's health care plan. Romney called him "angry", but the crowd -- and Republican voters watching at home -- most likely share Santorum's frustration.

Politico praised the performance:

. . . It's safe to say that on overall points, Santorum won the debate, although it was Romney who had the standout moment.

Santorum is barely making a play in Florida, and he is leaving the state this weekend to go home and handle his taxes -- essentially ceding the stage to Romney and Gingrich. But he has been presenting himself in this race as a more "consistent" conservative alternative to Gingrich, and someone who can match Romney on leadership.

Tuesday's closed primary will see one nominee gaining the full 50 Florida delegates. In the final debate, Romney's success at pressing his close rival Gingrich on issues that are contentious for them both -- transparency of personal wealth and immgration -- appears to have knocked him back into the lead.