Democratic Nebraska Senator Ben Nelson is retiring at the end of 2012.
News of Nelson’s retirement is especially tough for Democrats, given that outside groups poured over $1 million in ads on his behalf to shore up his standing in the state. The ads were also aired in hopes of convincing Nelson to run for a third term.
Republicans have aggressively targeted Nelson this year, and outside GOP groups had already begun pouring money into the state, hitting him over his vote for President Obama’s health care law.
Nelson was considered the most vulnerable Senate Democrat running in 2012.