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.

My friend Michael Tofias and I were talking about Nelson just the other day and he made what I think is a very astute remark: Nelson is probably the only sort of Democrat who could be elected to the Senate in a state like Nebraska. In other words, only a Democrat who doesn’t really seem like a Democrat to Democrats would be acceptable to the generally quite conservative populace of Nebraska.

Or, in other words, those Nebraskans who thought Nelson shouldn’t have even called himself a Democrat are likely to be even more disappointed going forward.

(Source: cognitivedissonance)