Winning Florida primary won't seal the deal for Mitt Romney Reporting from Jacksonville, Fla. - Four years ago, Mitt Romney lost the Florida presidential primary to John McCain by just 5 percentage points. Exactly nine days later, Romney dropped out of the GOP race. This time around, Romney is expected to win Florida, probably by substantially more than McCain did. But Romney's defeated rivals aren't going anywhere. Newt Gingrich has vowed to press on to the Republican National Convention at the end of August. Rick Santorum and Ron Paul are already campaigning in states that hold caucuses next month. The sharp contrast between Romney's 2008 pullout and his rivals' determination to press ahead -- into March, if not beyond -- reflects the changing forces that have reshaped Republican presidential politics. His opponents argue that the race needs to go on because Romney is a weak front-runner who has failed to rally every element of the party - especially its most conservative voters. But a more prosaic set of factors may be more to the point: An overhaul of the nominating rules and a radically reshaped campaign-finance environment are making it impossible for Romney to prevail as quickly as McCain did last time. At the same time, it arguably makes it easier for his challengers to keep going. In 2008, Romney abandoned his campaign, despite winning 11 states and having the personal resources to continue (he had already spent $40 million of his personal fortune, leaving him a mere $200 million or so). But the former Massachusetts governor had come to the conclusion that McCain was likely to be the nominee, and that continuing to fight might damage his own prospects for another presidential run in 2012. So, Romney quit on Feb. 7, two days after the Super Tuesday primaries. This year, however, Super Tuesday has been pushed back into March, part of a deliberate effort by party leaders to forestall a rush to judgment in choosing a nominee. Over the next 33 days, only two primaries with delegates at stake are being held -- Michigan, which Romney won last time, and Arizona, where he ran second to favorite-son McCain -- both on Feb. 28. The Missouri presidential primary on Feb. 7 is a nonbinding "beauty contest"; Gingrich didn't even make the ballot. Nevada, Colorado, Minnesota and Maine, all won by Romney in 2008, will stage caucuses this month, but relatively few delegates will be selected. The non-Romney candidates are already looking ahead to the first half of March, when 17 states hold voter tests. Gingrich is counting on March 6 victories in Georgia, Tennessee and Oklahoma, and in Alabama and Mississippi the following week. Romney is favored in Massachusetts and Virginia (where Gingrich also failed to qualify for the ballot) and Ohio. Ron Paul, with a grass-roots funding base and national organization of supporters, is targeting caucuses in an effort to win enough delegates to influence the platform at the national convention in Tampa. He also hopes to harvest delegates in primary states that award delegates to losing candidates - another change in party rules designed to extend the campaign. The Texas congressman could decide to keep going until June, when the last delegates are chosen. Gingrich and Rick Santorum, who have struggled to keep their campaigns solvent, are being propped up by "super PACs," funded by wealthy benefactors who can give in unlimited amounts thanks to a series of federal court rulings in 2010. In the past, when candidates stopped winning primaries, their money dried up and their campaigns were over. Not in 2012, at least not yet. The Gingrich campaign argues that, even with a Florida win, Romney will have less than 10% of the delegates needed to lock up the nomination. Realistically, no candidate will be able to accumulate the necessary 1,144 delegates before mid-April, at the earliest. If Romney runs the table in February and prevails in the first half of March, it will be extremely difficult for Gingrich or Santorum to credibly argue that they have a viable chance of heading him off. The pressure to quit would be even more intense than it's likely to be in coming days. On the other hand, if Romney stumbles -- or if Gingrich, perhaps with fresh backing from his wealthy Las Vegas benefactors, the Adelsons, decides to wage jihad against the party elite -- the race will go on, into April and perhaps beyond. Unlike Romney, four years ago, the 68-year-old Gingrich has little incentive to give up anytime soon. For the former House speaker, the future is now.