House Speaker-in-waiting John Boehner, voice breaking with emotion, declared shortly before midnight Tuesday that the results were "a repudiation of Washington, a repudiation of big government and a repudiation of politicians who refuse to listen to the people."
Obama monitored returns at the White House, then telephoned Boehner with congratulations in a call that underscored the power shift.
Incomplete returns showed the GOP picked up at least 57 House seats - the biggest party turnover in more than 70 years - and led for eight more, far in excess of the 40 they needed for a majority. Among the losers was Rep. Tom Perriello, a first-termer from Virginia for whom Obama campaigned just before the election.
On a night of triumph, Republicans also gained at least six Senate seats, and tea party favorites Rand Paul in Kentucky, Mike Lee in Utah and Marco Rubio in Florida were among their winners. But Christine O'Donnell lost badly in Delaware, for a seat that Republican strategists once calculated would be theirs with ease. And they lost the nation's most closely watched race, in Nevada, where Majority Leader Harry Reid was a winner in an especially costly and brutal campaign in a year filled with them.
The GOP also wrested nine governorships from the Democrats, Ohio and Pennsylvania among them. In New York, Andrew Cuomo won the office his father, Mario, held for three terms. And in California, Edmund G. Brown Jr., was successful in his bid for a comeback to the governor's office he occupied for two terms more than a quarter-century ago.
The biggest win was the House, a victory made all the more remarkable given the drubbing Republicans absorbed at the hands of Democrats in 2006 and again in 2008.
The takeaways came in bunches - five Democratic-held seats each in Pennsylvania and Ohio and three in Florida and Virginia.
Democrats conceded nothing while they still had a chance. "Let's go out there and continue to fight," Speaker Nancy Pelosi exhorted supporters in remarks before television cameras while the polls were still open in much of the country.
But not long after she spoke, Democratic incumbents in both houses began falling, and her own four-year tenure as the first female speaker in history was doomed. She gave no indication of her own plans.
With unemployment at 9.6 percent nationally, interviews with voters revealed an extraordinarily sour electorate, stressed financially and poorly disposed toward the president, the political parties and the federal government.
Sen.-elect Paul, appearing Tuesday night before supporters in Bowling Green, Ky., declared, "We've come to take our government back."
About four in 10 voters said they were worse off financially than two years ago, according to preliminary exit poll results and pre-election surveys. More than one in three said their votes were an expression of opposition to Obama. More than half expressed negative views about both political parties. Roughly 40 percent of voters considered themselves supporters of the conservative tea party movement. Less than half said they wanted the government to do more to solve problems.
Republicans were certain of at least six Senate pickups, including the seat in Illinois that Obama resigned to become president. Rep. Mark Kirk won there, defeating Alexi Giannoulias.
Democratic Sens. Russell Feingold in Wisconsin and Blanche Lincoln in Arkansas were turned out of office. In addition, Republicans scored big in races for Democratic seats without incumbents on the ballot. Former Rep. Pat Toomey won a close race in Pennsylvania, North Dakota Gov. John Hoeven won easily there, and former Sen. Dan Coats breezed in a comeback attempt for the Indiana seat he voluntarily gave up a dozen years ago.
"Republicans will continue to stand up for the American people and for the priorities they voted for today, and we are hopeful that the administration and Democrat leaders will change course," Republican Senate leader Mitch McConnell said in a written statement.
Democrats averted deeper losses when Gov. Joe Manchin won in West Virginia - after pointedly distancing himself from Obama - for the unexpired portion of the late Sen. Robert C. Byrd's term, and Attorney General Richard Blumenthal was victorious in Connecticut, dispatching Linda McMahon, former CEO of World Wrestling Entertainment. Sen. Barbara Boxer was elected to a fourth term in California, overcoming a challenge from Carly Fiorina.
The GOP gubernatorial gains came after a campaign in which their party organization spent more than $100 million, nearly double what Democrats had.
Among the incumbents who fell were Ted Strickland in Ohio, defeated by former Rep. John Kasich, and Chet Culver in Iowa, loser to former Gov. Terry Branstad.
In California, former Gov. Edmund G. Brown Jr. was elected to the office he held for two terms more than a quarter-century ago.
In a footnote to the brutal politics of the campaign, Republican-turned- independent Lincoln Chafee was elected governor of Rhode Island. Obama campaigned in the state in the campaign's final week. But he declined to endorse the Democratic candidate, Frank Caprio, out of what the White House said was respect for Chafee, who had endorsed the president in his own presidential race two years ago.
A Republican takeover of the House would usher in a new era of divided government after two years in which Obama and fellow Democrats pushed through an economic stimulus bill, a landmark health care measure and legislation to rein in Wall Street after the near collapse of the economy in 2008.
Republicans opposed all three of the measures, accusing the president of supporting an ever-expanding role for the government with ever-rising spending.
Paul's triumph in Kentucky completed an improbable rise for an eye surgeon making his first race. He drew opposition from the Republican Party establishment when he first launched his bid, then struggled to adjust to a statewide race with Attorney General Jack Conway.
Rubio, also running with tea party support, was gaining about 50 percent of the vote in a three-way race in Florida, months after he forced Gov. Charlie Crist to leave the Republican Party and run as an independent. Democratic Rep. Kendrick Meek was running third.
But a third tea party-backed candidate, O'Donnell, who went from a virtual unknown to primary winner to fodder for late-night comedians in the span of a few months, lost overwhelmingly to Democrat Chris Coons in Delaware. Republicans had counted on taking the seat from the Democrats early this year, but that was before O'Donnell defeated veteran Rep. Mike Castle in a September primary. Democrat John Carney easily won the seat that was Castle's for nearly two decades.
Not all the Republican newcomers were party crashers.
In New Hampshire, Republican Kelly Ayotte won a Senate seat, defeating Democratic Rep. Paul Hodes. Former Bush administration official Rob Portman won a seat in Ohio, and Rep. Jerry Moran won in Kansas and Rep. Roy Blunt in Missouri.
Democratic Sen. Patrick Leahy of Vermont was re-elected to his seventh term and Barbara Mikulski her fifth. New York Sens. Charles Schumer and Kirsten Gillibrand also won, as did Sen. Ron Wyden in Oregon and Boxer in California In Hawaii, Democratic Sen. Daniel Inouye was elected for a ninth time to the seat he has held since 1962.
Republican Sen. Jim DeMint, who won a second term in South Carolina, has been working to establish a nationwide standing among conservatives. He was instrumental in supporting tea party challengers in several primaries this spring and summer at a time the GOP establishment was backing other candidates.
In Alabama, Sen. Richard Shelby was re-elected easily, as were Republican Sens. Tom Coburn in Oklahoma, Richard Burr in North Carolina, John Thune in South Dakota, Johnny Isakson in Georgia and Mike Crapo in Idaho.
The president gave a series of radio interviews pleading with Democratic supporters not to sit on the sidelines. "I know things are still tough out there, but we finally have job growth again," he said in one. "It is all at risk if people don't turn out and vote today."
While Obama's name was not on the ballot, his record and policies were. After nearly two years in power, he and congressional Democrats were saddled politically with the residue of the worst recession since the 1930s.
"I will honestly say that I voted for him two years ago," said Sally McCabe, 56, of Plymouth, Minn., stopping to cast her ballot on her way to work. "And I want my vote back."
In Cleveland, Tim Crews, 42, said he measures Obama's performance by the number of paying miles he drives in his delivery van. His miles have tripled to 9,000 a month. Crews said of the economy: "It's moving. I know, because I'm moving it." He voted accordingly.
With so many contested races, and a Supreme Court ruling removing restrictions on political activity by corporations and unions, the price tag for the elections ran to the billions.
Much of the money paid for television advertisements that attacked candidates without letup, the sort of commercials that voters say they disdain but that polls find are effective.