Democratic Sen. Ben Nelson of Nebraska is expected to announce he will retire after two terms, hampering the Democrats' efforts to hold on to control of the Senate.
Nelson is scheduled to convene a news conference in Nebraska as early as today,
Politico reports, quoting insiders close to the Senate leadership.
Nelson was considered a struggling incumbent heading into the November election cycle, with the Democratic Senatorial Campaign Committee spending more than $1 million to bolster his image against GOP attacks.
Majority Leader Harry Reid of Nevada and Democratic Sen. Chuck Schumer of New York had tried to keep Nelson from retiring. The 70-year-old senator has more than $3 million in his campaign accounts, and his approval rating was holding steady.
Nelson's departure throws the race for control of the Senate up in the air. The GOP could take his seat easily, although popular former Sen. Bob Kerrey has talked about running. Other vulnerable Democrats include Sen. Claire McCaskill of Missouri and Jon Tester of Montana, although the Democratic Party thinks they are winnable seats.
In all, 23 Democratic-controlled seats are up for grabs in November, while Republicans have to defend only 10. The GOP needs just four new seats to take control of the Senate.
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