Liberal Massachusetts was rocked when Republican Scott Brown rode a wave of voter anger to defeat Democrat Martha Coakley in a US Senate election that left President Barack Obama's healthcare overhaul in doubt and marred the end of his first year in office.
The loss by the once-favoured Ms Coakley for the seat held by the late Senator Ted Kennedy for nearly half a century signalled big political problems for the president's party in the autumn when House of Representatives, Senate and gubernatorial - governorship - candidates are on the ballot nationwide.
More immediately, Mr Brown will become the 41st Republican in the 100-member Senate, which could allow the Republicans to block the Obama healthcare legislation and the rest of his agenda.
Democrats needed Ms Coakley to win for a 60th vote to thwart Republican procedural manoeuvres to block votes on the controversial legislation.
The election transformed reliably Democratic Massachusetts into a battleground state.
A day before the first anniversary of Mr Obama's swearing-in, it played out amid a backdrop of animosity and resentment from voters over persistently high unemployment, industry bailouts, exploding government budget deficits and partisan wrangling over healthcare.
Even before the polls closed at 1am GMT, administration officials were privately accusing Ms Coakley of a poorly-run campaign and playing down the notion that Mr Obama or a toxic political landscape had much to do with the outcome.
Ms Coakley's supporters, in turn, blamed that very environment, saying her lead dropped significantly after the Senate passed healthcare reform shortly before Christmas and after the Christmas Day attempted airline bombing that Mr Obama himself said showed a failure of his administration.
With the stakes so high, Mr Obama campaigned for Ms Coakley in Boston over the weekend and appeared in television ads on her behalf.
Mr Obama has made overhauling the US healthcare system, which leaves nearly 50 million people uninsured, his top domestic priority. Mr Kennedy was a long-time champion of the cause.