Boston, Massachusetts (CNN) -- In a stunning upset that reshaped the U.S. political landscape, Republican Scott Brown won Tuesday's special election in Massachusetts for the U.S. Senate seat formerly held by liberal Democrat Ted Kennedy.





Brown defeated Democrat Martha Coakley, the state attorney general.





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 due to brain cancer last August. Before Kennedy won the seat for the first time in 1962, his older brother John held it for nearly eight years until his election as U.S. president in 1960.





"This really does change everything, you know that?" said Mitt Romney, the former GOP governor of Massachusetts who introduced Brown at his victory rally.





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Voters across Massachusetts braved winter cold and snow for an election with high stakes -- the domestic agenda of President Obama, including his top domestic priority, health care reform.





Brown's victory strips Democrats of their 60-seat Senate super-majority, needed to overcome GOP filibusters against future Senate action on a broad range of White House priorities. Senate Democrats needed all 60 votes in their caucus to pass the health care bill, and the loss of one seat now imperils generating that support again for a compromise measure worked out with the House.





"Forty one, forty one," chanted the crowd at Brown's rally, referring to his new status as the Senate's 41st Republican. Brown, a state senator until now, heralded his victory as the start of more election surprises in 2010.





No Republican had won a U.S. Senate race in Massachusetts since 1972, and Democrats control the governorship, both houses of the state legislature, and the state's entire congressional delegation.





"When there's trouble in Massachusetts, rest assured there's trouble everywhere, and they know it," Brown said of the Democratic Party.





Republican leaders sounded a similar theme, saying Americans were fed up with what they called Democratic arrogance in Washington.





"Americans are investing their hopes in good Republican candidates to reverse a year-long Democrat trend of ignoring the American people on the issues of health care, spending and the growth of government," Senate Minority Leader Mitch McConnell, R-Kentucky, said in a statement.





The seat vacated by Kennedy's death is currently held by his former aide and longtime friend Paul Kirk, who was appointed on an interim basis.





Obama called Brown and Coakley on Tuesday night, and a White House statement said the president "told Sen. Brown that he looks forward to working with him on the urgent economic challenges facing Massachusetts families and struggling families across our nation."





Massachusetts Secretary of State Bill Galvin said last week that certifying Tuesday's election results could take more than two weeks -- potentially enough time to allow congressional Democrats to pass a final health care bill before Brown is seated.





But multiple Democratic sources said that is unlikely. Even if House and Senate Democrats could reach a deal to meld their bills and pass them in the next couple of weeks, there would be a huge outcry from not only Republicans, but also an increasingly distrustful public if they appeared to be rushing it through.





Galvin had predicted as many 2.2 million of the state's 4.5 million registered voters would vote -- at least double the turnout from December's primary. In one sign of high interest, more than 100,000 absentee ballots were requested ahead of the election, according to Brian McNiff, Galvin's spokesman.





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





Until recently, Brown was underfunded and unknown statewide. Waging a nationally backed campaign that included driving his pickup around the state, Brown surged in the weeks preceding Tuesday's vote and led in all the final polls.





In a sign of the high stakes involved, the Coakley campaign held an afternoon news conference Tuesday to complain that voters in three places received ballots already marked for Brown.





McNiff confirmed that the secretary of state's
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