As Republican presidential candidates prepare to debate in Orlando, the GOP race is down to Mitt Romney v Rick Perry

One thing has become clear as the GOP presidential candidates prepare for their third debate in three weeks: the Republican nomination has come down to Mitt Romney versus Rick Perry.

Debate fatigue may be setting in but tonight's encounter could see more fireworks. In the previous debates this month Rick Perry found himself in the unaccustomed role of punching bag, as the other candidates took turns on assailing his positions on social security, immigration and the HPV vaccine in Texas.

Expect Perry to come out fighting this time around, as he has done when winning three bitterly-contested gubernatorial primaries in Texas. In particular he is likely to target Romney, his nearest rival in what the opinion polls show to be a two-horse race.

Michele Bachmann, once the Tea Party's shining star, has been on the wane since she erupted on the scene in June. Former Speaker of the House Newt Gingrich appears to be on a vanity mission. One-time Utah governor Jon Huntsman has little to show for his moderate message. Businessman Herman Cain, who benefitted from a flicker of excitement early on, has made few gains.

Only Ron Paul – the veteran Texas libertarian now running an increasingly slick and conventional campaign compared with his 2008 attempt – is making any national progress against the Romney-Perry duopoly although he can't yet be said to be challenging either candidate.

It's true that polling primaries four months out from election day is fraught with peril – ask Hillary Clinton what good her 2007 support did for her come 2008 – because of the difficulties of locating likely voters and tiny sample sizes. But with the Republican field now settled and the clock ticking, the dynamics of the race seem to assure a Perry versus Romney contest.

Tonight's debate in Orlando is significant because it takes place in a key battleground state, both for the Republican primaries and the 2012 general election. And in the Sunshine State, Perry appears to be doing well, despite Romney's repeated attacks on Perry's description of social security as a "Ponzi scheme".

A poll of Florida Republicans by Quinnipiac University, released today, shows Perry supported by 32% and Romney by 21% (assuming Sarah Palin doesn't enter the contest).

None of the other Republican candidates can rate higher than 8%, with Gingrich, Cain and Bachmann followed by Paul in sixth place.

Across the other side of the country, a new poll of Arizona Republicans also put Romney and Perry far ahead of the pack, with Romney on 31% and Perry on 25% – and the rest nowhere to be found, Bachmann polling 5% and Paul again back in 6th.

Two polls from New Hampshire show a different picture: both ARG and Suffolk University show Mitt Romney in a commanding lead – unsurprisingly, given Romney's strong ties to the state – with Perry struggling and Ron Paul's message doing well in the "Live free or die" state.

One word of warning: a letter sent from Sarah Palin's political action committee to supporters earlier this week said the former Alaska governor was "on the verge of making her decision of whether or not to run for office," and asked for donations.

With Palin, anything is possible – including a September surprise.