Boston, Massachusetts (CNN)  -- Republican Scott Brown won a major upset victory in Tuesday's special election for the U.S. Senate seat formerly held by liberal Democrat Ted Kennedy. Brown defeated Massachusetts Attorney General Martha Coakley, the Democratic candidate. Brown's victory made real the once unthinkable prospect of a Republican filling the seat held by Kennedy, known as the liberal lion, for almost 47 years until his death from brain cancer in August. Voters across Massachusetts braved winter cold and snow for an election with high stakes -- the domestic agenda of President Obama, including his priority of health care reform.
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Democrat Martha Coakley concedes to Republican Scott Brown
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President Obama "frustrated" by Massachusetts Senate race, aide says
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Good turnout expected as Massachusetts votes to fill Sen. Ted Kennedy's seat
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Democrats would lose filibuster-proof majority in Senate with Brown win
Ted Kennedy
Kennedy
Ted Kennedy
Coakley was initially expected to easily win the race to replace @placeholder, who made health care reform the centerpiece of his Senate career.
Scott Brown
Brown
Brown
Scott Brown
Brown
However, @placeholder surged in the weeks preceding Tuesday's vote and led in all the final polls.
Obama
Obama
"If you were fired up in the last election, I need you more fired up in this election," @placeholder urged a crowd at a Coakley campaign rally on Sunday.
Martha Coakley
Martha Coakley
He promised at a rally Sunday that, if elected, he would back tax cuts and be tougher on terrorists than @placeholder.
Martha Coakley
Martha Coakley
Voters more concerned with the economy were split almost evenly between the two candidates; voters more worried about health care narrowly supported @placeholder.
Scott Brown
Brown
Brown
Scott Brown
Brown
@placeholder's surprising strength came in part because some independents and conservatives who have supported Democrats in the past were having second thoughts.
Martha Coakley
Martha Coakley
Several Democratic sources say multiple Obama advisers have told the party they believed @placeholder was going to lose, despite Obama's campaign appearance for Coakley on Sunday.
Martha Coakley
Martha Coakley
Several Democratic sources say multiple Obama advisers have told the party they believed Coakley was going to lose, despite Obama's campaign appearance for @placeholder on Sunday.