COLUMBIA, S.C. (AP) – U.S. Sen. Lindsey Graham is taking on three little-known GOP challengers in the next step of a race already on pace to become the most expensive in South Carolina history. Tuesday’s primary election is the last marker ahead of an expected general election face-off with Democrat Jaime Harrison. Graham faces fellow Republicans Duke Buckner, Michael Lapierre and Joe Reynolds. Buckner is an attorney and former Walterboro city councilman. Lapierre is a retired corporate executive from Pickens. Both have argued that Graham isn’t conservative enough. Reynolds is a Merchant Marine engineer from Charleston. He has said new leadership is needed in Washington. Graham is seeking his fourth term.