The 2010 governor’s contest in South Carolina is shaping up to be a proxy war for 2008 GOP presidential candidates.

Mitt Romney’s endorsement of state Rep. Nikki Haley on Tuesday pits his candidate against three hopefuls aligned with other 2008 presidential candidates.

Former Sen. Fred Thompson (R-Tenn.) is backing Rep. Gresham Barrett (R-S.C.), Mike Huckabee is backing Lt. Gov. Andre Bauer and Sen. John McCain (R-Ariz.) is a close ally of state Attorney General Henry McMaster.

All four candidates are huddled within about 15 points of each other in most polling on the race, making it a wide-open affair.

Of course, Huckabee and Romney have a little more skin in the game, as South Carolina is a key presidential primary state, and they may have designs on running again in 2012. Among other potential candidates, former Sen. Rick Santorum (R-Pa.) and Rep. Mike Pence (R-Ind.) are both backing Barrett.

Minnesota Gov. Tim Pawlenty and former Alaska Gov. Sarah Palin have yet to weigh in.