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
Coakley was initially expected to easily win the race to replace @placeholder, who made health care reform the centerpiece of his Senate career.
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.