Washington (CNN) - While issuing a harsh critique of the partisanship that often has the Senate in gridlock, Olympia Snowe, a three-term moderate Republican from Maine, stunned her colleagues Tuesday when she announced she would not seek re-election.
Her unexpected decision could make it more difficult for hopeful Republicans to win back the majority in the chamber where Democrats currently hold a 53-47 seat advantage.
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"I do find it frustrating," Snowe said in a statement, "that an atmosphere of polarization and 'my way or the highway' ideologies has become pervasive in campaigns and in our governing institutions."
Snowe, 65, is one of just a handful of reliably moderate senators - from either party – who regularly worked across the aisle and often voted with the other side. For instance, she provided just one of three critical Republican votes for President Obama's fiscal stimulus plan in 2009, helping the controversial plan pass.
"Unfortunately, I do not realistically expect the partisanship of recent years to change over the short term. So at this stage of my tenure in public service, I have concluded that I an not prepared to commit myself to an additional six years in the Senate, which is what a fourth term would entail," she said.
Sen. Susan Collins, Maine's other moderate Republican senator, said Tuesday she was "devastated" to learn Snowe was leaving the Senate.
"Olympia could always be counted on as a leader who sought solutions, not political advantage," Collins said in a statement.
The decision caught Democrats off guard too.
"Whoa," said Sen. Chuck Schumer of New York, a Democratic leader, when told the news in the Capitol.
"She's a good lady and an example of sometimes how the roughness of the political world can affect things," he said. "She's great and she'll be missed by people on both sides of the aisle."
Asked about Democrats' chances to pick up the seat, Schumer declined to predict.
"I'm not going to talk about that," he said.
In her statement, Snowe insisted she would have won re-election but didn't have the stomach to remain in Washington. While she faced a tea party primary opponent Republican leaders felt confident the popular Snowe would have beaten back that challenge.
Sen. John Cornyn, R-Texas, who heads the Senate Republican campaign committee, issued a statement praising Snowe but also vowing to hold her seat.
"Maine has a proud history of electing independent leaders, including a Republican governor in 2010, and while this will be a key battleground in the Fall, I am confident it will remain in Republican hands," he said.
Snowe was not available for interviews Tuesday but an aide said she plans to address the media later in the week in Maine.