Veteran US Congressman Mark Souder has resigned from the House of Representatives over an affair with a member of his staff.
The eight-term Indiana Republican said he had sinned against God, his wife and his family by having a "mutual relationship" with the staff member.
In a statement, he said he was quitting in order to avoid putting his family through a "painful, drawn-out process".
He said he would now focus on repairing his marriage and his faith.
Mr Souder is described by the Associated Press news agency as a social conservative and strong advocate of gun rights.
His constituency, Indiana's Third District, has been strongly contested by Democrats in the past, the agency notes.