"Clearly there's a lot of momentum and a lot of incentive for people to work together to really find answers to the challenges," she said.
The vanquished Republican, former Massachusetts Gov. Mitt Romney, tried to set a more conciliatory tone on the way off the stage.
"At a time like this, we can't risk partisan bickering," Romney said after a campaign filled with it. "Our leaders have to reach across the aisle to do the people's work."
Obama won at least 303 electoral votes to 206 for Romney, with 270 needed for victory, and had a near-sweep of the nine most hotly contested states.
But the close breakdown in the popular vote showed Americans' differences over how best to meet the nation's challenges. With more than 90 percent of precincts reporting, the popular vote went 50 percent for Obama to 48.4 percent for Romney, a businessman-turned-politician. Romney had argued that Obama failed to turn around the economy and he said it was time for a new approach that combined lower taxes and a less intrusive government.
Obama's re-election means his signature health care overhaul will endure, as will the Wall Street overhaul enacted after the economic meltdown. The drawdown of troops in Afghanistan will continue apace. With an aging roster of justices, the president probably will have at least one more nomination to the Supreme Court.
A second term is sure to produce turnover in his Cabinet. Treasury Secretary Timothy Geithner has made it clear he wants to leave at the end of Obama's first term but is expected to remain in the post until a successor is confirmed. Secretary of State Hillary Rodham Clinton, Obama's rival for the presidency four years ago, is ready to leave. Defense Secretary Leon Panetta isn't expected to stay on.
Obama won even though exit polls showed that only about 4 in 10 voters thought the economy is getting better, just one-quarter thought they're better off financially than four years ago and a little more than half think the country is on the wrong track.
But even now, four years after George W. Bush left office, voters were more likely to blame Bush than Obama for the fix they're in.
Some Americans were hopeful for progress in Obama's second term.
"He may not have done a great job in my mind but I kinda trust him," Jerry Shul said Wednesday morning in Times Square. "And I feel like he's gonna keep trying and I feel like when people keep trying in you favor things work out. I have faith in him, I have faith he will get with the Republicans and get something done."
Elsewhere on the ballot, voters in Maine and Maryland became the first to approve same-sex marriage by popular vote while Washington state and Colorado legalized recreational use of marijuana.
The most expensive presidential campaign in history, at $2 billion plus, targeted people in the nine states that determined the outcome, and the two sides drenched voters there with more than a million ads, the overwhelming share of them negative.
Obama claimed at least seven of those states, most notably Ohio, seen as the big prize. He also prevailed in Iowa, New Hampshire, Colorado, Nevada, Virginia and Wisconsin. Romney got North Carolina.
Florida was too close to call Wednesday morning. The unofficial count had Obama with a 46,000-vote lead, but Florida historically has left as many as 5 percent of its votes uncounted until after Election Day.
Overall, Obama won 25 states and the District of Columbia. Romney won 24 states.
It was a more measured victory than four years ago, when Obama claimed 365 electoral votes to Arizona Sen. John McCain's 173, and won 53 percent of the popular vote.
Preliminary figures indicate fewer people participated this time. Associated Press figures showed that about 118 million people had voted in the White House race, but that number will rise as more votes are counted. In 2008, 131 million people voted, according to the Federal Election Commission.