Sen. Ben Nelson (D-NE) is set to announce on Tuesday that he will retire in 2012, a Democratic source has confirmed to TPM.
Nelson was already probably the most vulnerable Democratic incumbent going into 2012, and Republicans and GOP-aligned groups were already advertising against him.
Holding this seat could be difficult for Democrats, as the state voted 57%-42% for John McCain in 2008, and has not voted Democratic for president since the 1964 Lyndon Johnson landslide.
Nelson’s retirement was first reported by Politico.
One potential Democratic candidate for the seat might be former Sen. Bob Kerrey, whom Nelson succeeded in 2000. On the Republican side, there has already been an active primary between state Attorney General Jon Bruning, former state Attorney General Don Stenberg (whom Nelson defeated in 2000), and state Sen. Deb Fischer — but Republicans have also been trying to recruit Gov. Dave Heineman.
Nelson was first elected in 2000, by a 51%-49% margin, and was re-elected by 64%-36% in the heavily Democratic year of 2006. Nelson had previously served two terms as governor, from 1990-1998, but also lost the 1996 open-seat Senate race by a 10-point margin.