Updated 5:02 p.m.
Sen. Ben Nelson, D-Neb., announced Tuesday that he is retiring after two terms in office, a move that is a serious blow to Democrats' hopes of maintaining its slim Senate majority. His decision turns what would have been a competitive red-state Senate race into a very likely GOP pickup next year.
"While I relish the opportunity to undertake the work that lies ahead, I also feel it's time for me to step away from elective office, spend more time with my family, and look for new ways to serve our state and nation," Nelson said in a videotaped statement. "Therefore, I am announcing today that I will not seek reelection. Simply put: It is time to move on."
Despite Democratic hopes that former Democratic Sen. Bob Kerrey will run again for the seat, Democrats have described Nelson running again as the only way to hold the seat.
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"There is no Plan B in Nebraska," a Democratic leadership aide said this month.
Nelson's retirement is especially tough for Democrats, given that Democratic 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.
"Over the course of his career, Ben's commitment to working with both Democrats and Republicans across a broad range of issues is a trait far too often overlooked in today's politics," President Obama said in a statement. "Michelle and I commend Ben for his service, and wish him and his family well in the future."
"For more than two decades, Senator Nelson has been a loyal public servant to the people of Nebraska and he will be missed here in the US Senate. Republicans will continue to have their hands full with a very divisive primary in the state, which will provide an opportunity for Democrats to remain competitive," said Democratic Senatorial Campaign Committee Chair Patty Murray, who notably stopped short of expressing confidence in a victory in the Cornhusker State.
Republicans have aggressively targeted Nelson this year, and outside GOP groups had already begun spending money against Nelson, hitting him over his vote for President Obama's health care law.
Nelson looked in decent shape for re-election, according to his campaign's own polling. In early December, Nelson released a poll showing his favorability was on the rise and that he improved his standing against Republican opponents. Democratic groups credited the ad campaign for improving his favorables.
But throughout the last month, Nelson continued to face a barrage of attacks from the opposition. Crossroads GPS decided to drop more than more than $500,000 against Nelson in the state's two largest media markets. Americans for Prosperity purchased $120,000 on cable television for anti-Nelson ads. And Nelson's likely Republican opponent, Attorney General Jon Bruning, launched an ad of his own earlier this month, in which he contrasts himself with Nelson.
Even with Nelson in the race, the senator was considered the most vulnerable Democrat up for re-election, given the conservative nature of his state. With Nelson out of the race, Republicans hold a clear edge here. The Democratic bench is weak in the state, though some operatives have discussed the possibility that former Sen. Bob Kerrey could run again.
Bruning is the frontrunner in the Republican primary, which also includes Treasurer Don Stenberg, state Sen. Deb Fischer, and businessman Pat Flynn. Bruning leads in fundraising and polls.
"Ben Nelson has been a dedicated public servant of the state of Nebraska for over two decades. I wish him and his family well in their future endeavors," Bruning said on Monday.
There was speculation Gov. Dave Heineman could still enter the Republican race, he had framed a potential run as something he would consider if he had to in order to turn the seat Republican -- something that wouldn't be necessary with Nelson taking a pass on reelection.