The battle for Florida is one between a heavily-funded, well-organized campaign – Mitt Romney's – and the one with the momentum coming out of South Carolina: Newt Gingrich.

Romney has had a big team in place since at least September, knocking on doors, drawing up lists of potential supporters and organizing absentee voters. He has a head-start among the 4 million registered Republicans. About 450,000 absentee ballots have been sent out, of which at least a quarter have been returned. The Romney team has contacted most of them, and according to rough estimates is winning by two to one.

Gingrich had only a token team of 14 in place and is virtually starting from scratch.

But, as Romney has found in 2008 and again in 2012, organization and money do not guarantee success, and Florida has to be viewed as a toss-up.

The polling, has veered dramatically over the last couple of weeks, underlines that. As the Gingrich momentum grew in South Carolina, the Florida polls saw him catch up then reverse Romney's commanding lead, and the former speaker arrived in the state last weekend with some giving him a lead of nine points. But over the past few days that trend, too, has gone into reverse, and the latest surveys all point to a slight lead for Romney.

Florida is one of the most important swing states, not only for the Republican primaries but for the White House: remember the "hanging chads" from the 200 election? President Barack Obama won with only a margin of 2.8% in 2008, and the state may be pivotal again in November 2012, which is why the Republicans have opted to hold their convention in Tampa in August.

It is going be a tough election for President Obama in Florida, given that the state has suffered badly from the recession and the housing crisis. The scale of the housing repossessions is the main reason Romney is pushing hard on Gingrich's involvement with mortgage giants Freddie Mac and Fannie Mae, who are frequently blamed for the collapse of the housing market.

The state has almost 19 million people and is closer in make-up to the rest of America than the first three contests in Iowa, New Hampshire and South Carolina. Although geographically in the south, the psychology of the state is different, in part because of the large number of retirees from New York and elsewhere in the north seeking the sun – 17% of the population is over 65 – and also because of its large proportion of Latinos of Cuban descent. The northern, rural part of the state tends to be closer in thinking to other southern states than more liberal Miami.

Its politics are diverse but overall the population is more interested in fiscal rather than social conservatism, which should be a plus for Romney.

Given the size of the state, the kind of retail politics seen in the first two contests, and to some extent in South Carolina, are difficult in Florida, and so more rests on advertising. In the days running up Tuesday's primary, this will come as close to saturation as possible. The problem for Romney and Gingrich is not so much the cost, but finding any more television or radio outlets to air adverts.

Ron Paul, who is largely ignoring Florida, estimated the cost of mounting a campaign in the state at $9 million, almost all of it on advertising. But even this $9 million estimate has already been shattered. Romney and his supporters have paid out $13 million for ads either already aired or to be aired over the next week. Gingrich, with $6m at the ready and more cash coming in, will attempt to match this.

The fourth candidate in the race, Rick Santorum, does not have the money to compete in the advertising market, which encompasses 10 separate media centers, and his brand of social conservatism does not resonate outside the northern part of the state. He may quit the race after Florida, though he has said he will fight on.

Florida used to have 100 delegates at stake, a big prize in the battle for the nomination. But because it moved its primary forward, in contravention of Republican party rules, it has been punished, and will have instead only 50 delegates instead. It is also winner-takes-all, rather than being awarded proportionally. This is the reason that Paul opted against spending much time in Florida, instead concentrating his efforts elsewhere, where he can pick up a share of delegates.

For Romney and Gingrich it is another critical test. If Gingrich wins here, he becomes the frontrunner for the party presidential nomination. If Romney wins, he is back on course, with a series of contests coming up that – on paper at least – seem more favorable to him. One excitable story this week had the headline "Florida is Armageddon". In fact, for the candidates and the Republican race, Florida is all about momentum.

Intellpuke: You can read this article by Guardian Washington, D.C., Bureau Chief Ewen MacAskill, reporting from Miami, Florida, in context here: www.guardian.co.uk/world/2012/jan/26/florida-primary-money-momentum-gop