Sen. Jeff Bingaman, D-N.M., won't seek reelection in 2012.
"The end of this Congress is the right time for me to step aside and allow someone else to serve," Bingaman said in a statement Friday. "It is not easy to get elected to the Senate, and it is not easy to decide to leave the Senate."
The five-term senator becomes the third Democrat to announce retirement from the senate ahead of the 2012 elections.
Two Republicans have said they won't seek reelection. Texas Senator Kay Bailey Hutchison and Arizona Senator Jon Kyl both announced their retirements recently. Republicans wasted no time drawing conclusions about Bingaman's reported retirement.
"Like the earlier retirements in North Dakota and Virginia, Senator Bingaman's decision immediately presents another strong pickup opportunity for Senate Republicans," National Republican Senatorial Committee spokesman Brian Walsh said in a statement. "It also further limits the ability of national Democrats to play offense when their resources will be spread out over such an expansive defensive map."
But Bingaman seemed confident that his party could hold on to his seat after he leaves.
"I think the D's will hang on to my seat. And I'm going to do all I can to ensure that this remains a Democratic seat," Bingaman said Friday at his retirement press conference.
He also said he spoke Thursday night with Senate Majority Leader Harry Reid, D-Nev., and White House Chief of Staff Bill Daley about his decision to retire.
Elena Isella contributed to this report.