In a move that surprised political observers, Maine GOP Senator Olympia Snowe, who’s been in Congress since 1979, announced today that she won’t seek re-election.

In announcing her plans, Snowe, 65, emphasized that she is in good health and was prepared for the campaign ahead. But she said she was swayed by the increasing polarization in Washington.

“Unfortunately, I do not realistically expect the partisanship of recent years in the Senate to change over the short term,” Snowe said in a statement. “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.”

This is a huge blow to the GOP’s chances of retaking control of the US Senate. Alongside Elizabeth Warren’s surely hard-fought marquee race against GOP Scott Brown for Ted Kennedy’s Senate seat, the Maine seat is likely to turn blue.

From David Nir at DKE:

Whatever the cause, Snowe’s departure creates an enormous pickup opportunity for Democrats in this decidedly blue state. While several lesser-known candidates had been running against her (including former SoS Matt Dunlap, state Rep. Jon Hinck and state Sen. Cynthia Dill), expect a lot more interest now from bigger names, such as Reps. Chellie Pingree and Mike Michaud. This is going to be a huge contest and it automatically makes Republican hopes of re-taking the Senate that much more distant.

Mainer Joe Sudbay says this at Americablog:

This can only be good for Democrats. I imagine Congresswoman Chellie Pingree is taking a look at this opening. I hope she is.

As a Mainer, I’ve followed Snowe’s career for years. I never got the fascination people had with her. She’s had a long career in public service — and has had taxpayer funded benefits for all those years, too. When she and her new husband, then-Governor, John McKernan, got married back in 1989, they used her campaign funds to pay for the wedding reception.

Chellie Pingree is wealthy and could conceivably self-fund, making this Democratic pickup cost-free as well for the national party. Harry Reid and Patty Murray must be having a celebratory evening tonight.

UPDATE: The 2010 election, which saw the Maine legislature go GOP and LePage become governor with less than 40% of the vote in a three-way race, is viewed as an anomaly. Personal loyalty has kept the Maine Twins in office, not partisan loyalty. Maine is a blue state.