In Ohio, Democratic Sen. Sherrod Brown survived an onslaught of outside spending, some $30 million, to defeat state treasurer Josh Mandel. In Pennsylvania, Democratic Sen. Bob Casey survived a late scare from businessman Tom Smith, who invested more than $17 million of his own money in the race.
Democratic Rep. Chris Murphy won the Connecticut Senate 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.
Texas sent tea party-backed Ted Cruz to the Senate as the Republican won the seat held by retiring GOP Sen. Kay Bailey Hutchison. Cruz will become the third Hispanic in the Senate, joining Sen. Bob Menendez, D-N.J., and Marco Rubio, R-Fla.
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 in Maryland and Tom Carper in Delaware were all re-elected. Cruising to another term were Democratic Sens. Debbie Stabenow in Michigan, Kirsten Gillibrand in New York, Amy Klobuchar in Minnesota and Menendez in New Jersey..
In West Virginia, Democratic Sen. Joe Manchin won a full term even though his state went heavily for Republican presidential nominee Mitt Romney.
Tennesseans gave Republican Sen. Bob Corker a second term. Wyoming voters did the same for Sen. John Barrasso, and Republican Roger Wicker captured another term in Mississippi.
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.
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 Lieberman.
Republicans had to deal with retirements in Arizona, Texas and Maine.
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 and $40 million in Wisconsin in addition to $33 million in Ohio - reflected the high-stakes fight for the Senate.