U.S. Senator Ben Nelson, a conservative Democrat of Nebraska, announced on Tuesday that he will not seek re-election next year, a move that could make it harder for Democrats to retain the Senate majority.
"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," the 70-year-old senator said in a statement.
"Therefore, I am announcing today that I will not seek re- election. Simply put: It is time to move on," he said.
Nelson's retirement could deal a blow to Democrats' efforts to maintain control of the upper chamber. While he would have faced a tough re-election campaign next year, the incumbent senator is believed to be the most competitive Democrat in the race.
Democrats currently have a 53-47 advantage over Republicans in the Senate, including two independents who caucus with them. Among a total of 33 Senate seats up for grabs next year, 23 are held by Democrats and independents, compared with 10 held by Republicans.
Nelson was first elected to the Senate in 2000 and got re- elected in 2006. Before that, he was a two-term governor of Nebraska.