Republicans are likely to take over the Senate after Tuesday´s midterm battle, as they seized three key Democratic seats.
With most polls closed in the east, confident Republicans celebrated after the early victory of Senate Minority Leader Mitch McConnell, who could lead the chamber if the GOP wins a majority.
Republicans also emerged victorious in West Virginia and South Dakota, states which have shifted conservative in recent years, marking the first two of six pickups that the party needs in order to take control of the 100-member Senate.
They earned a third when incumbent Democrat Mark Pryor fell to young Iraq war veteran Tom Cotton in Arkansas, a state not even local hero president Bill Clinton could save from the Republican tide.
Democrats went into the poll holding a 55 to 45 seat advantage in the Senate and defended must-hold New Hampshire, where Senator Jeanne Shaheen repulsed Republican challenger Scott Brown.
The results showed Obama´s adversaries on course to win a majority in both chambers of Congress for the first time since 2006 and blight the president´s last two years in office.
Republicans have held the House of Representatives since 2010, and they had it safely in hand Tuesday.
Democrats — working feverishly to draw voters to the polls in a last-gasp effort to stave off disaster — could lose Senate seats in as many as 10 of the 36 states in play.
With no legislative base in Congress, Obama will struggle to pass any reforms in the final stretch of his mandate, and his opponents will be able to thwart his appointments to judicial and official posts.