More than $1 billion is projected to have been spent in Senate races by candidates and outside groups, according to the Center for Responsive Politics. But unlike in the 2010 and 2008 elections, neither party dramatically altered the balance of power in the Senate after this election.
Democrats defended 23 of the 33 seats in the Upper Chamber that were on the ballot in this election.
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Several retirements in Maine, Connecticut, Wisconsin, Arizona, Nebraska, New Mexico, Texas and Virginia imperiled some historically Democratic and Republican seats but opened opportunities in others.
The Democrats' achievement was aided in no small part by several high-profile missteps on the part of Republican candidates.
Embattled Democratic Sen. Claire McCaskill in Missouri faced a serious challenge from Todd Akin until his candidacy was imperiled by his comments suggesting that the human body could terminate a pregnancy that resulted from "legitimate rape."
The comments arguably aided McCaskill by refocusing the attention on her challenger, who was urged to drop out of the race by Republicans immediately after his remarks.
ABC News projects that McCaskill has won that race.
And in Indiana, tea party Republicans and many members of the GOP establishment actively campaigned against their incumbent, Sen. Dick Lugar, and instead nominated the state's Treasurer, Richard Mourdock, a candidate Democrats preferred.
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Mourdock received the personal endorsement of Mitt Romney in an ad late in the election, but his campaign ran into trouble when he said in an October debate that "even when life begins in that horrible situation of rape, that it is something that God intended to happen."
The comments set off a firestorm of recriminations from Democrats, and quickly prompted an apology from Mourdock.
ABC News projects that the Democratic nominee Rep. Joe Donnelly will win the Indiana Senate seat.
The gain in Indiana helped offset the loss of an open Democratic seat in Nebraska to Republican Deb Fischer, according to ABC News projections.
In other races, the slog was long and difficult.
A highly anticipated Massachusetts contest between Democratic activist and Harvard Law School professor Elizabeth Warren and Republican Sen. Scott Brown became one of the most expensive and closely watched races in the country.
Brown's seat became a target for Democrats who hoped to retake it after he won a special election after the death of longtime Democratic Sen. Ted Kennedy.
Brown, who ran and won in 2010 as a small-government conservative during a wave Tea Party-driven elections, ran a markedly more moderate race in 2012.
But returning to its blue-state roots, Massachusetts will elect Warren, ABC News projects.
In the current Congress, two independents caucus as Democrats. Angus King, who won the open Republican Senate seat in Maine as an independent, according to ABC News projections, has not said whether he will vote with the Democratic Party.
- Politics & Government