COLUMBIA, S.C. – Republican U.S. Sen. Jim DeMint, a favorite among tea party activists who has backed challenges to centrist veterans he didn't view as conservative enough, said Thursday he was resigning to take the helm of a conservative think tank.

The South Carolina lawmaker said in a statement he was stepping down to become president of the Heritage Foundation. His office said he would take the new job effective Jan. 1.

DeMint was first elected to the Senate in 2004 and easily re-elected six years later. He previously served in the U.S. House of Representatives for three terms.