WASHINGTON - Everyone loves a dark horse. And that goes double when it comes to presidential politics. Although being crowned the front-runner in a fight for the presidential nod conveys some benefits (money and media attention, mostly), there is something the electorate loves about getting behind an unknown candidate and riding him (or her) from worst to first - or close to it. James K. Polk is widely regarded as the original dark horse. His opponents mocked his anonymity - 'Who is James K. Polk?' - but he went on to become the country's 11th president. Dark horses populate modern presidential politics as well. In 2004, former Vermont Gov. Howard Dean began the Democratic nomination fight as a blip on the radar screen (and even that may be overstating where he began the race). But, capitalizing on the anger toward President George W. Bush within the Democratic Party, Dean rode a populist wave to the top of the field - until the wave broke just before the Iowa caucuses. Four years later, another former small-state governor - Arkansas' own Mike Huckabee - used his charisma and credentials as a social conservative to win in Iowa before ultimately fizzling out against Sen. John McCain, R-Ariz., in the GOP primary. As a result of his 2008 showing, Huckabee won't be able to claim dark horse status this time. So recent history then suggests that the 2012 Republican presidential field - one devoid of a clear front-runner - will produce a dark horse of its own. But who will it be? Here are four candidates who could fill the role: - Rick Santorum: The former senator from Pennsylvania has a niche - he's beloved by social conservatives - that might give him a base of support in the Iowa caucuses and the South Carolina primary. Santorum, who lost his reelection bid badly to Sen. Robert Casey, D-Pa., in 2006, is an underrated candidate on the stump and probably would do enough to stand out at least once on a crowded debate stage. It's hard to imagine Santorum broadening his support beyond his (relatively) narrow swath of social conservatives, but he could still help sway the race toward someone else. - Mike Pence: House members don't have much luck in presidential races; they typically suffer from a lack of a national fundraising base and a stature gap with their better-known rivals. Pence, an Indianan who resigned from House leadership after the election to presumably pursue a presidential bid, is seen by his allies as one of the few potential candidates who is acceptable to fiscal and social conservatives. And Pence has wowed at some of the early 2012 campaign cattle calls with a blunt speaking style that resonates with voters. - Scott Brown: The Massachusetts Republican, who became a national star this year when he won a special election to replace the late Sen. Ted Kennedy, D-Mass.), will face serious political peril in the Bay State if he chooses to run for reelection. Democrats are already lining up to challenge him and Republicans' inability to win the governor's race or the open 10th District in November has to be a discouraging sign for Brown. Given that - and his proven skills as a candidate - it's not entirely implausible that he could decide to run for national office instead. - Marco Rubio: Sure, Rubio won't even be sworn into the Senate until early next year. And, yes, he's only 39. But the Florida senator-elect is already a national star, a conservative favorite and a proven fundraiser ($18 million - at least - collected for his campaign). Barack Obama changed the calculus for all rising political stars when he beat the first family of Democratic politics in the 2008 primary and then won 365 electoral votes in the general election. If no candidate emerges as a front-runner by summer of 2011, Rubio might go from dark horse to pole position. 