Three-term Maine Republican Olympia Snowe, a mavericky moderate known for her willingness to vote across party lines, announced this afternoon that she will not seek another term in 2012. In a statement, Snowe insisted it was not the prospect of losing that worried her — Snowe was being challenged by two tea party candidates — but the blizzard of partisanship that has essentially frozen the Senate:

"With my Spartan ancestry I am a fighter at heart; and I am well prepared for the electoral battle, so that is not the issue. However, what I have had to consider is how productive an additional term would be. Unfortunately, I do not realistically expect the partisanship of recent years in the Senate to change over the short term. So at this stage of my tenure in public service, I have concluded that I am not prepared to commit myself to an additional six years in the Senate, which is what a fourth term would entail."

Snowe's retirement is not just a sad day for Maine/a wonderful day for snow-related puns. It boosts the chances that the Democrats, who are defending many more seats this year than Republicans are, will be able to cling to control of the Senate, now that they face an open seat and not a popular incumbent. Her retirement is, in a way, one last middle finger to party loyalty.