Washington ( CNN ) -- Republican Sen. Olympia Snowe of Maine announced Tuesday she will retire rather than seek re-election this year , surprising colleagues and perhaps casting the future of her seat in doubt . The decision was made `` after an extraordinary amount of reflection and consideration , '' she said in a statement . Snowe , who turned 65 last week , was first elected to the U.S. House in 1978 and then to the Senate in 1994 . She is the first woman to serve in both chambers of a state legislature and the U.S. Congress . Snowe was known as a moderate who sometimes sided with Democrats in the increasingly partisan environment of Washington politics . Her statement cited the partisan divide . `` I have no doubt I would have won re-election , '' Snowe said , describing her political service in Maine and Washington as `` an indescribable honor and immeasurable privilege . '' While her motivation and sense of responsibility remain , she continued , `` I do find it frustrating , however , that an atmosphere of polarization and 'my way or the highway ' ideologies has become pervasive in campaigns and in our governing institutions . '' `` Unfortunately , I do not realistically expect the partisanship of recent years in the Senate to change over the short term , '' Snowe said . `` 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 . '' The White House released a statement praising Snowe 's bipartisan efforts . `` For almost four decades , Olympia Snowe has served the people of the great state of Maine . ... From her unwavering support for our troops , to her efforts to reform Wall Street , to fighting for Maine 's small businesses , Sen. Snowe 's career demonstrates how much can be accomplished when leaders from both parties come together to do the right thing for the American people . '' Initial reaction from colleagues indicated Snowe 's decision was unexpected . `` I was surprised . I know that she 's been quite frustrated with the lack of civility in Washington and the fact that she 's a bridge builder -- and it was more and more difficult to do that . But we were all surprised here in Maine that she would make the decision , '' said Maine GOP Chairman Charlie Webster . `` It 's going to shake things up in Maine politics . '' Maine Sen. Susan Collins , a moderate Republican , said she was `` devastated '' to learn of Snowe 's decision not to seek re-election . `` I know this was an incredibly difficult decision for Olympia , '' said Collins , who lauded Snowe as `` a leader who sought solutions , not political advantage . '' Democratic Sen. Chuck Schumer of New York expressed surprise at the news when told by CNN . `` We 'll miss her , '' Schumer said . `` She 's a good , good lady and an example of ... sometimes how the roughness of the political world can affect things . She 's great , and she 'll be missed by people on both sides of the aisle . '' With Snowe in the race , two of the top political handicappers -- the Cook Political Report and the Rothenberg Political Report -- had considered the seat `` safe Republican '' in the November election . Democrats hold a 53-47 majority in the Senate but are defending 23 of the 33 seats up for grabs in November , including those of two independents who caucus with the Democrats . Guy Cecil , executive director of the Democratic Senatorial Campaign Committee , called Snowe 's departure an `` unexpected opportunity . '' `` Maine is now a top pick-up opportunity for Senate Democrats , '' Cecil said in a statement . `` If there is one place in the country that is likely to reject the extreme , anti-middle class , divisive Republican agenda it is Maine . Democrats not only hold a strong registration advantage in the state , but this is a state that the president won by 17 points in 2008 and will likely win by a significant margin this year , as well . '' However , Texas Sen. John Cornyn , the chairman of the National Republican Senatorial Committee , said his party remains `` well-positioned to win back a Senate majority in November . '' `` Maine has a proud history of electing independent leaders , including a Republican governor in 2010 , and while this will be a key battleground in the fall , I am confident it will remain in Republican hands , '' Cornyn said in a statement . The Maine GOP chairman said it 's too early to tell yet whether Democrats could potentially pick up the seat . `` We 've got a number of qualified people that could run , '' said Webster . Two Republican candidates already announced primary challenges to Snowe -- former Lisbon Falls Selectman Scott D'Amboise and tea party activist Andrew Ian Dodge . In addition , two Democrats being mentioned as potential candidates were businesswoman and 2010 gubernatorial candidate Rosa Scarcelli and state Rep. Emily Cain . U.S. Rep. Chellie Pingree , D-Maine , was also hailed as a possible candidate . The Progressive Change Campaign Committee launched a campaign shortly after Snowe 's announcement to draft the Democratic representative into running . The group , which claims 6,000 members in Maine and close to a million nationwide , praised Pingree for having a `` bold progressive voice . '' CNN 's Ted Barrett , Deirdre Walsh , Rebecca Stewart , Tom Cohen and Shannon Travis contributed to this report .
White House praises Sen. Olympia Snowe for her bipartisan leadership . Previously known as moderate Republican who sometimes voted with Democrats . Maine GOP chairman says the decision is going to shake up Maine politics . She cites the partisan divide in Maine as a reason for decision .