Updated: 1:33 p.m.Senate Republican Policy Committee Chairman John Ensign (Nev.) is stepping down from his leadership position after acknowledging an affair with a former campaign aide.Ensign spoke with Minority Leader Mitch McConnell (R-Ky.) Wednesday about the scandal and his future in the Conference, and the two men agreed that Ensign would step aside as the No. 4 leader in the GOP hierarchy. Ensign, who served as National Republican Senatorial Committee chairman in the 2008 cycle, was elected Policy Committee chairman last year.”Sen. Ensign and Sen. McConnell talked this morning and Sen. Ensign came to the conclusion that it was in the best interests of his family and the conference if he stepped aside as chairman of the Policy Committee,” the aide said.In a brief statement, McConnell accepted Ensign’s resignation.“He’s accepted responsibility for his actions and apologized to his family and constituents. He offered, and I accepted, his resignation as chairman of the Policy Committee,” McConnell said.It wasn’t immediately clear who would vie to replace Ensign, but the most likely contender is Sen. John Thune (S.D.), now the Conference vice chairman. Other possibilities could include Sens. Lisa Murkowski (Alaska), Johnny Isakson (Ga.) or Richard Burr (N.C.). However, all four of those Senators are up for re-election in 2010, a factor that could influence any decision to enter a leadership race.Ensign admitted his affair at a news conference Tuesday in Nevada. He didn’t speak directly to his future as a U.S. Senator, but he said he remains “committed to my service in the United States Senate.—The Nevada Republican, up for re-election in 2012, was seen as rising star in the Conference and a possible candidate for the presidential nomination in 2012.But Wednesday’s decision to step aside in the Senate leadership is almost certain to complicate if not derail any of his higher ambitions.In his admission Tuesday, Ensign said he had an extramarital affair with a former campaign aide whose husband was also a former Ensign staffer. The relationship took place between December 2007 and August 2008.