Maine Democratic Rep. Chellie Pingree has opted not to run for retiring Sen. Olympia Snowe’s seat.

“After careful consideration I have decided to run for re-election to the U.S. House this year,” she said in a statement. “There is much at stake in this election and although the prospect of running for and possibly serving in the United States Senate was very exciting, in the end I concluded that I will best serve the people of Maine by running for re-election to the House.”Maine Democrats over the last days expressed fears about the Independent candidacy of former Gov. Angus King and how that would affect Democratic prospects for picking up the Republican-held seat. But when asked on Tuesday, Democratic Senatorial Campaign Committee Chairwoman Patty Murray (Wash.) would not rule out the possibility that King would caucus with Democrats — increasing speculation that the former governor could become the de facto Democrat in the race.

Pingree had “taken out papers” from the state secretary of state’s office, which is the first step in launching a campaign in Maine. But that move was made prior to her decision because of the approaching filing deadline on March 15.

The decision will be a major letdown for her liberal base. The Progressive Change Campaign Committee and MoveOn.org were out front hours after Snowe’s announcement encouraging Pingree to run.

The Congresswoman is the second serious Democratic contender to shy away from the race. Rep. Mike Michaud, who represents the state’s more conservative 2nd district, announced last week he would not be seeking the Democratic nod after taking the first steps toward building a campaign.

As late as Thursday, it appeared likely that the two Maine Members were waiting for each other to blink so one could run for the seat.

Republicans mulling the open-seat contest are Maine Secretary of State Charlie Summers, state Treasurer Bruce Poliquin and Attorney General William Schneider.

Roll Call currently rates this race as Tossup.