Sen. John Ensign, R-Nev., announced Thursday he would step down from his position next month in the midst of an ethics investigation.
The Senate Ethics Committee is investigating an affair between Ensign and his former political treasurer, Cynthia Hampton. Her husband, Doug, also worked with Ensign in his legislative office.
Both were dismissed in 2008, but Ensign and his family provided the Hamptons nearly $100,000 and assistance in finding new jobs in Las Vegas.
The committee has been investigating the case for over 22 months and plans to complete its work in a timely fashion despite Ensign's resignation, Sen. Barbara Boxer, D-Calif, said in a statement, according to the Washington Post.
Politico reports Ensign's resignation means the committee cannot bring any formal charges against him, but can refer it to criminal investigation to the Justice Department if it so chooses.
Nevada Gov. Brian Sandoval is allowed to appoint a Republican to fill Ensign's seat until his term ends.
Ensign was not planning on running for re-election, so Sandoval's appointment will influence next year's election. The New York Times is reporting a likely choice is Rep. Dean Heller, who was already running for the seat.