South Carolina Democrat Jim Rex, the state Superintendent of Education, is now an official candidate for the 2010 election to succeed term-limited Republican Mark Sanford as governor.

Rex’s bid, which he had earlier signaled, adds a statewide elected official to the crowded June Democratic primary field. His party is trying to overcome South Carolina’s usual Republican leanings — and take advantage of the turmoil surrounding Sanford, who has declined demands even from many fellow Republicans that he resign following his confession of an extramarital affair and allegations that he improperly used state-funded travel.

Rex didn’t reference Sanford directly as he launched his campaign with an op-ed piece in The State newspaper in Columbia and in a statement on his campaign Web site. But a reference to the incumbent appeared clear in Rex’s lament about the “seemingly endless distractions” that “have crippled our state government.”