Republican Sen. John Ensign of Nevada has stepped down from his leadership post one day after admitting he carried on a marital affair with a woman who was on his campaign staff.

Ensign conveyed his decision in a phone call with Senate Republican Leader Mitch McConnell, who said he had accepted the resignation.

Ensign was chairman of the Republican Policy Committee, the fourth-ranking spot in the leadership.

He remained away from the Capitol during the day, and aides declined to answer additional questions about the affair.

A timeline issued Tuesday said Ensign was involved in a "consensual affair" from December, 2007 through August, 2008. There has been no indication of why the senator decided to announce his infidelity when he did.