Republicans seized control of the House on Tuesday and shrank the Democratic advantage in the Senate, dealing a major setback to President Obama and sweeping a number of "tea party" insurgents into power.
The nearly coast-to-coast blowout -- a result of voters' frustration and deep economic anxiety -- promised to once more change the country's political dynamic, presenting challenges to both parties in a newly divided government.
Obama, who pushed through the most expansive legislative agenda of any president in generations, could spend the remainder of his term just trying to preserve what he has accomplished. Republicans, with a measure of power, will share some responsibility for governing and may have to do more than simply thwart the president and his fellow Democrats -- or face a similar repudiation by voters in 2012.
Republican leader John A. Boehner of Ohio, who is line to replace San Francisco Democrat Nancy Pelosi as the next House speaker, struck a notably somber tone as he spoke to supporters in Washington.
"This is not a time for celebration," he said. "Not when 1 in 10 of our fellow citizens are out of work. Not when we buried our children under a mountain of debt. Not when our Congress is held in such low esteem."
Obama, who called Boehner around midnight to give his congratulations, planned to offer his reaction at a news conference Wednesday.
The election results, a likely gain of 60 or more seats for Republicans, were like a steam release after months of building pressure and amounted to the biggest turnover since the GOP won 52 House seats in 1994 -- the last time Democrats controlled both Congress and the presidency.
Republicans won House seats in virtually every part of the country, gaining bunches in the hard-pressed industrial Midwest and toppling incumbents in Virginia, Texas, New Hampshire and Florida.
The Democrats fared better in races for the Senate, hanging onto the majority by a handful of seats. Their leader, Harry Reid of Nevada, was reelected by a surprisingly comfortable margin over tea party favorite Sharron Angle.
The Senate contests produced mixed results for the nascent tea party movement. Rand Paul, a founder of the Kentucky branch, notched a victory, Marco Rubio won in Florida and Mike Lee won in Utah.
But Christine O'Donnell lost in Delaware, a seat both parties had put in the GOP category until the centrist Rep. Michael N. Castle lost the Republican primary. In Nevada, Angle was seen as the weakest of Reid's potential opponents.
Voters also chose governors in 37 states, electing Democrats Jerry Brown in California and Andrew Cuomo in New York. Republican Nikki Haley posted a tea party victory in South Carolina and the GOP ousted Democrat Ted Strickland in Ohio.
In some ways, Democrats were fighting political forces beyond their control. Midterm elections are inevitably a referendum on the party holding the White House and almost always result in congressional losses.
This year, Democrats were defending a sizable number of incumbents, having picked up more than 50 House seats in the last two elections, including many in GOP-leaning districts. That put the party on the defensive from the start.
On top of that, the economy was the worst it had been in over a generation, with unemployment approaching 10% and bankruptcy and home foreclosure rates soaring. The result was a combustible mix of nervousness and anger; about 4 in 10 voters said they were worse off financially than two years ago, according to exit polls.
The party's problems were exacerbated by the ambitious -- critics called it overreaching -- agenda pursued by Obama and the Democrats controlling Congress. They muscled through a massive healthcare overhaul, bailed out the auto industry and passed an $800-billion economic stimulus bill, all in about a year's time.
The president and his allies said the measures were needed to rescue the economy from its worst downturn since the Great Depression, and Obama argued right through election day that the measures were working.
"Things have gotten better over the last two years," Obama said in a round of interviews Tuesday with radio stations in several key states. "We can only keep it up if I've got some friends and allies in Congress and statehouses."
But critics said the Democrats had exploited the financial crisis to wrench the country too far left, expanding the size and scope of the government in ways most Americans never imagined when they embraced Obama's promise of change back in 2008. They urged voters to push back at polls.
Republicans were vague, promising tax and spending cuts without offering much detail or explaining how they would reduce the federal deficit.
But that seemed not to matter. Unsettled voters were looking to vent their displeasure and Democrats were the obvious target; more than 1 in 3 voters polled said they cast their ballots to express unhappiness with Obama.