Unless something unexpected takes place, Florida can already claim the top spot in deciding recent presidential nominations, both for Republicans and Democrats, and is poised to be, along with a handful of states, a pivotal swing state in the November elections.
As for determining nominations, Florida now has replaced both Iowa and South Carolina as the "must-win" early state. In 2008, Barack Obama's win in Iowa certainly gave him the boost that later exploded into momentum in the South Carolina Democratic contest. But had Florida's legislature not moved the Florida contest ahead in the order of states voting that year, leading to an announced Democratic National Committee decision not to seat any of its delegates, all of Florida's delegates would have counted in the contest between Hillary Clinton and Barack Obama.
Clinton was poised to cream Obama in the Sunshine State and in fact did so, while having to stick to a pledge not to campaign in Florida. Had the contest been held anytime after February 5th of that year, momentum likely would have shifted and Clinton would have received the nomination. In this instance, Florida's lack of participation (Florida finally sent a diminished delegation to the convention well after Obama had secured the nomination) was the critical ingredient in helping make Barack Obama his party's nominee.
The 2008 contest for the Republican nomination was far more cut and dried. Former Gov. Mike Huckabee roared out of Iowa with a big win. But with an upset comeback in New Hampshire and a tight victory in South Carolina, John McCain won the endorsement of a then-popular incumbent Gov. Charlie Crist and basically cruised towards the GOP nomination after a win in Florida.
That leads us to 2012. Minus some amazing changes in the political landscape, Mitt Romney, who basically saw the last of his hope for the nomination in 2008 go down the drain in Florida, essentially had his "game change" moment in the state's 2012 primary. With Rick Santorum, surprising all with his performance in Iowa, and Newt Gingrich winning big in the "always the ultimate nominee" South Carolina, Romney unleashed funds, ads, a strong organization, and two comeback Florida based debates and sent Gingrich packing with a huge victory.
While Santorum had moments of appearing to present a continued challenge, Romney's position was likely strengthened beyond measure in later states because of his Florida knockout punch. He became the strongest candidate, and to republican voters, he seemed the most likely to give Obama a run for his money.