Two years after Obama swept into the White House, voter anxiety about the economy and discontent with his leadership fueled big Republican gains that toppled Democratic House Speaker Nancy Pelosi from power and ushered in a new era of divided government.

Television networks projected Republicans would pick up at least 50 House seats, more than the 39 they need for a majority that would elevate conservative John Boehner to House speaker and slam the brakes on Obama's agenda.

It was the biggest shift in power since the 1994 Republican landslide gave them a 54-seat House gain when Democratic President Bill Clinton was in power.

Republican control of even one chamber of Congress would likely spark legislative gridlock, weakening Obama's hand in fights over the extension of soon-to-expire income-tax cuts and the passage of comprehensive energy or immigration bills.

In the Senate, Democrats held the late Robert Byrd's seat in West Virginia and appeared likely to retain at least a narrow Senate majority.

Republicans picked up three Democratic seats in Indiana, North Dakota and Arkansas, but needed to sweep six crucial toss-up Senate races, including those in Democratic-leaning California and Washington, to seize majority control.

All 435 House seats, 37 of the 100 Senate seats, and 37 of the 50 state governorships are at stake in Tuesday's voting.

Florida Republican Marco Rubio and Kentucky Republican Rand Paul became the first Tea Party-backed candidates to win Senate seats, ensuring an influx of conservative views in the staid chamber. Another Tea Party favorite, Republican Christine O'Donnell in Delaware, lost her race.