President Barack Obama rolled to re-election and a second term in the White House on Tuesday with a victory over Republican challenger Mitt Romney as the Democrat overcame deep doubts about his handling of the U.S. economy.
Romney, closeted with advisers in Boston, did not immediately concede defeat because of questions about whether Obama had really won the pivotal state of Ohio. But other projected Obama victories in Virginia, Nevada, Iowa and Colorado carried the president past the 270 electoral votes needed for victory.
Obama, America's first black president, won by convincing voters to stick with him as he tries to reignite strong economic growth and recover from the worst recession since the Great Depression of the 1930s. An uneven recovery has been showing some signs of strength but the country's 7.9 percent jobless rate remains stubbornly high.
Obama's victory in the hotly contested swing state of Ohio - as projected by TV networks - was a major step in the fight for the 270 electoral votes needed to clinch the White House and ended Romney's hopes of pulling off a string of swing-state upsets.
Obama scored narrow wins in Ohio, Wisconsin, Iowa, Pennsylvania and New Hampshire - all states that Romney had contested - while the only swing state captured by Romney was North Carolina, according to television network projections.
The nationwide popular vote remained extremely close.
There was no immediate word from the Romney camp on the reported results, with some Republicans questioning whether Obama had in fact won Ohio despite the decisions by election experts at all the major TV networks to declare it for the president.
The later additional of Colorado and Virginia to Obama's tally - according to network projections - meant that even if the final result from Ohio is reversed, Romney still could not reach the needed number of electoral votes in America's state-by-state system of choosing a president.
While Obama supporters in Chicago were ecstatic, Romney's Boston event was grim as the news was announced on television screens there. A steady stream of people left the ballroom at the Boston convention centre.
At least 120 million American voters had been expected to cast votes in the race between the Democratic incumbent and Romney after a campaign that was focused on how to repair the ailing U.S. economy.
The same problems that dogged Obama in his first term are still there to confront him again.
He faces a difficult task of tackling $1 trillion annual deficits, reducing a $16 trillion national debt, overhauling expensive social programs and dealing with a gridlocked U.S. Congress that kept the same partisan makeup.
THE NEXT FOUR YEARS
Obama's victory will set the country's course for the next four years on spending, taxes, healthcare, the role of government and foreign policy challenges such as the rise of China and Iran's nuclear ambitions.
Each man offered different policies to cure what ails America's weak economy, with Obama pledging to raise taxes on the wealthy and Romney offering across-the-board tax cuts as a way to ignite strong economic growth.
Whether both Democrats and Republicans will now be able to come together and craft a compromise is an open question as Republican congressional leaders vow to stick to their pledges not to raise taxes on anyone.
Inside Obama's Chicago campaign headquarters, staffers erupted into cheers and high fives as state after state was called for the president.
Romney, who would have become America's first Mormon president, made last-minute visits to Ohio and Pennsylvania on Tuesday to try to drive up turnout in those states, while Vice President Joe Biden was dispatched to Ohio.
Republicans are likely to face questions about their ability to appeal to non-white voters as Hispanics, a growing minority, voted heavily for the president.
Obama's Democrats held their Senate majority, while Romney's Republicans retained House of Representatives control.
Democrat Claire McCaskill retained her U.S. Senate seat from Missouri, beating Republican congressman Todd Akin, who stirred controversy with his comment in August that women's bodies could ward off pregnancy in cases of "legitimate rape.
Democrats gained a Senate seat in Indiana that had been in Republican hands for decades after Republican candidate Richard Mourdock called pregnancy from rape something that God intended. Democratic congressman Joe Donnelly won the race.
In another high-profile Senate race, Democrat Elizabeth Warren, a law professor who headed the watchdog panel that oversaw the government's financial sector bailout, defeated incumbent Massachusetts Republican Senator Scott Brown.
Former Maine Governor Angus King won a three-way contest for the Senate seat of retiring Republican Olympia Snowe. King ran as an independent, but he is expected to caucus with Democrats in what would amount to a Democratic pick-up.
Florida Democratic Senator Bill Nelson easily beat back a challenge from Republican congressman Connie Mack to win a third term, while Democratic congressman Chris Murphy beat Republican Linda McMahon, a businesswoman who had served as chief executive of a professional wrestling company.
(Additional reporting by Jeff Mason in Chicago, Patricia Zengerle in Boston, Edith Honan in New York, Brendan O'Brien in Milwaukee, Dave Warner in Philadelphia, Philip Barbara in New Jersey, Matt Spetalnick, Lisa Lambert, Susan Heavey, Thomas Ferraro, Susan Cornwell, Anna Yukhananov and Roberta Rampton in Washington; Writing by Steve Holland and John Whitesides; Editing by Claudia Parsons and Will Dunham)