The Nevada Republican, who has been embattled since revealing he had an affair with the wife of a former aide, was facing a possible primary challenge from Rep. Dean Heller (R). Heller is now expected to run for the open Senate seat.
Ensign was facing growing pressure to exit the Senate race, and he has mounting legal bills related to his admission of the extramarital affair. He is the eighth Senator and third Republican to announce retirement this Congress. To see who else is leaving, check out our Casualty List.
Roll Call Politics currently rates the Nevada Senate race as a Tossup.
Senate Minority Leader Mitch McConnell, R-Ky., carries a musket on stage as he speaks during the American Conservative Union's Conservative Political Action Conference (CPAC) at National Harbor, Md., on Thursday March 6, 2014.