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 romped to victory 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 a 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.
But North Carolina, another Democratic must-win, remained too close to call as the votes were counted.
And in Virginia, a race few experts had considered in play, Democrats were bracing for a shock potential upset of their incumbent Senator Mark Warner.
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. The only question was whether Republicans would dramatically extend their lead there.
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.
The party of an incumbent president historically fares badly in elections in his second term, and every president since Ronald Reagan has left office with the opposition controlling Congress.
The Republicans essentially based their campaigns on attacks against Obama and policies like his troubled health care reform.
Despite steady economic improvements, the national mood is far from buoyant.
A CNN exit poll showed 79 percent disapproved of Congress and less than one-third were satisfied with the Obama administration or with Republican leaders.
But McConnell, who brushed aside the toughest challenge to his seat in 30 years, sounded a conciliatory note in his victory speech.
“This experiment in big government has lasted long enough. It’s time to go in a new direction,” McConnell said, but added “we do have an obligation to work together on issues where we can agree.”
WORST MAP FOR DEMOCRATS:
Perhaps bracing for the inevitably ugly outcome, Obama has invited the four congressional leaders, including McConnell, to meet him at the White House on Friday.
While Republicans are likely to cooperate on issues like tax reform, the party will seek to breathe life into their stalled jobs bills, to gain approval of the delayed Keystone XL pipeline, roll back some carbon emission regulations and tweak Obamacare.
Voters were also electing dozens of state governors and hundreds of local legislators and deciding dozens of state-level issues, including in some places the legalization of marijuana.
However successful the Republicans are, a complete picture may not emerge Tuesday.
There are strong prospects for runoffs in Democrat-held Louisiana and Republican-held Georgia, where rules require a second round if winners do not earn more than 50 percent of the vote.
Add to that a probable days-long ballot count in remote Alaska, where there is an unpredictable and tight race.
Louisiana’s runoff would be on December 6, but a Georgia runoff would be on January 6, which means senators may not know who controls the chamber when Congress opens January 3. (AFP)