(CNN) -- The Vital Center is under siege on Capital Hill. "Congress is now more polarized than at any time since the late 19th century," attests the data-driven blog Vote View. It has gotten so bad that Sen. Olympia Snowe is throwing in the towel on her three-term career in disgust: "I do find it frustrating," she said, "that an atmosphere of polarization and 'my way or the highway' ideologies has become pervasive in campaigns and in our governing institutions." What's worse, she doesn't think it's going to get better any time soon: "I do not realistically expect the partisanship of recent years in the Senate to change over the short term."
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John Avlon: Fed up with partisan dysfunction, Olympia Snowe not seeking re-election
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She is among politicians targeted by own party for being centrist, a damaging trend, he says
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GOP may live to regret this, he says: Her leaving will make it tough to regain the Senate
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Avlon: This should be wake-up call for moderate Americans
"We must return to an era of civility in government driven by a common purpose to fulfill the promise that is unique to @placeholder."