Sen. Olympia Snowe announced today that she is retiring from the Senate, citing the partisanship of Washington as her reason for not running for re-election.

“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,” the Maine Republican said in a statement.

“Unfortunately, I do not realistically expect the partisanship of recent years in the Senate to change over the short term,” she added. “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.”

Roll Call Politics had rated this race as Safe Republican. Snowe’s decision means that the race is seriously in play for Democrats. She was first elected to the Senate in 1994 and won her last re-election in 2006 with 74 percent of the vote.