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.
Former Sen. Scott Brown, R-Mass., candidate for U.S. Senate in New Hampshire, holds his hand over his heart during the singing of the national anthem as he waits to take the stage for his town hall campaign rally with Sen. John McCain at the Pinkerton Academy in Derry, N.H., on Monday, Aug. 18, 2014.