Angus King, an independent candidate, was projected the winner of the Maine Senate race to fill the seat being vacated by Republican Sen. Olympia Snowe by the AP.
King was favored over GOP contender Charlie Summers and Democratic hopeful Cynthia Dill going into Election Day.
Before voters hit the polls on Tuesday, speculation had already begun to swirl over which party King would caucus with if elected to the upper congressional chamber.
Here's more from the AP:
Independent Angus King captured a Republican-held Senate seat in Maine on Tuesday, adding a dose of uncertainty to the fight between majority Democrats and the GOP for control of the Senate.
King prevailed over Republican Charlie Summers and Democrat Cynthia Dill in the race to replace Republican Sen. Olympia Snowe, who blamed partisan gridlock in Washington for her unexpected decision to retire after 18 years in the Senate. The Associated Press called the race based on interviews with voters as they left polling stations.
In Connecticut, Democratic Rep. Chris Murphy won the seat held by Sen. Joe Lieberman, the independent who was the Democratic Party's vice presidential nominee in 2000. Murphy's win marked the second straight defeat for former wrestling executive Linda McMahon, who spent $50 million of her own wealth in a failed effort against Sen. Richard Blumenthal in 2010 and more than $42 million this election cycle.
In Florida, Democratic Sen. Bill Nelson triumphed in his bid for a third term, holding off a challenge from Republican Rep. Connie Mack. Republican groups had spent heavily against Nelson early in the race, but the moderate Democrat was a prolific fundraiser with wide appeal among Democrats and some Republicans in the Panhandle.
Independent Sen. Bernie Sanders won a second term in Vermont. Democratic Sens. Sheldon Whitehouse in Rhode Island, Ben Cardin was in Maryland and Tom Carper in Delaware were all re-elected. Tennesseans gave Republican Sen. Bob Corker a second term.
King has resolutely refused to say which party he'd side with if elected, and the outcome of the presidential election and the final Senate lineup could influence his decision. Members of both parties have indicated that they expect King – former governor and one-time Democrat who supports President Barack Obama – to align with Democrats. One factor could be the million-plus dollars that Republican-leaning groups such as the U.S. Chamber of Commerce and Karl Rove's organization spent on ads criticizing King.
Democrats currently hold a 53-47 edge in the Senate, including the two independents who caucus with them. Republicans need a net of four seats to grab the majority, three if Republican Mitt Romney wins the presidency.
The caustic campaign for control of the Senate in a divided Congress was marked by endless negative ads and more than $1 billion in spending by outside groups on races from Virginia to Montana, Florida to New Mexico. The outcome in Ohio and Virginia was closely linked to the presidential race. Republicans and Democrats in Massachusetts, North Dakota and Montana hoped that energetic campaigns and personality would lead to ticket-splitting by voters.
Republicans were on the defensive in Indiana, where tea party-backed state treasurer Richard Mourdock was locked in a close race with Democratic Rep. Joe Donnelly.
With 30 percent of the vote, Donnelly held a narrow lead, 48 percent to 46 percent. Libertarian Andrew Horning, a potential factor in the final results, grabbed the remainder.
Mourdock had been considered the favorite after knocking out six-term Sen. Richard Lugar in the GOP primary in May. But he damaged his chances when he said in a debate that pregnancy resulting from rape is "something God intended."
Republican Sen. Scott Brown, who stunned Democrats in January 2010 by capturing Sen. Edward M. Kennedy's Massachusetts seat, was the underdog against Democrat Elizabeth Warren in one of the nation's costliest races. The two candidates agreed to no outside money by super PACs and other independent groups then together spent $68 million on their campaign.
The arithmetic was daunting for Democrats at the start of the election cycle – they had to defend 23 seats to the GOP's 10. Further complicating the calculation were Democratic retirements in Virginia, Wisconsin, North Dakota, Hawaii, Nebraska and New Mexico as well as the retirement of independent Connecticut Sen. Joe Lieberman, the Democratic vice presidential nominee in 2000.
Republicans had to deal with retirements in Arizona, Texas and Maine.
Republican hopes of reclaiming the Senate suffered a major blow when the GOP candidate in Missouri made awkward remarks about rape and abortion.
Democratic Sen. Claire McCaskill was considered the most vulnerable incumbent, but Republican Rep. Todd Akin severely damaged his candidacy in August when he said women's bodies have ways of avoiding pregnancy in instances of "legitimate rape." GOP leaders, including Romney, called on him to abandon the race. Akin stayed in and is counting on support from evangelicals to lift his prospects in a state that favors Romney.
Democrats and Republicans in a dozen states faced an onslaught of outside money that financed endless negative commercials and ugly mailings that left voters exasperated. The record independent spending – $50 million in Virginia, $40 million in Wisconsin and $33 million in Ohio – reflected the high-stakes fight for the Senate.
In the closing days of the campaign, polls showed a tightening race in Ohio where Democratic Sen. Sherrod Brown faced a challenge from state treasurer Josh Mandel and in Pennsylvania where Democratic Sen. Bob Casey tried to fend off businessman Tom Smith, who invested more than $17 million of his own money..