South Carolina state Sen. Vincent Sheheen cemented his front-runner standing among the Democratic field for governor when House Minority Leader Harry Ott decided not to join the race and instead throw his support behind Sheheen.

But Sheheen might not enjoy that lead position much longer, with State Superintendent of Education Jim Rex waiting in the wings, and likely to jump in the race to succeed Republican Gov. Mark Sanford, who is term-limited in 2010.

Rex, who has said he’ll make a decision by Labor Day, has already begun drawing endorsements from local Democratic officials.

Ott had long been eyeing a run, as well, but issued a release Tuesday saying that it was Sheheen who would make the state’s best chief executive. “On the issues that will define the success or failure of our next governor – particularly creating good jobs and revitalizing our public schools – Vincent is the candidate with the independence, experience and vision to move South Carolina forward,” Ott said of his former House colleague and friend.