President Barack Obama was re-elected president Tuesday night, put over the top by the crucial battleground state of Ohio following the most expensive election in U.S. history.
"You made your voice heard, and you made a difference," Obama told supporters.
"I will return to the White House more inspired and more determined than ever," he said. 'We've got more work to do."
Obama and his family walked onto stage at his Chicago headquarters to the strains of Stevie Wonder's "Signed, Sealed, Delivered." The crowd welcomed him by chanting, "Four more years!"
A roar of approval thundered through the crowd after NBC reported that Ohio had gone to Obama. The victory in Ohio put Obama at 274 electoral college votes, four more than needed.
"This happened because of you. Thank you," Obama tweeted to supporters. It was retweeted more than more than 318,000 times, a record. A picture posted around 11 p.m. EST on Obama's Facebook page showing him hugging first lady Michelle Obama under the headline "Four more years" was liked by more than a million users.
Mitt Romney was silent for more than an hour after Ohio was projected for Obama. But he then conceded in a phone call to Obama.
"I have just called President Obama to congratulate him on his victory," Romney told disappointed supporters. "I wish all of them well, but particularly the president, the first lady and their daughters. This is a time of great challenges for America, and I pray that the president will be successful in guiding our nation."
Earlier, Pennsylvania, Wisconsin and New Hampshire went to Obama, according to NBC News, and Romney took North Carolina. Obama also won Virginia, Ohio and Colorado. Votes were still being counted in Florida.
After the Obama victories in Pennsylvania and Wisconsin, U.S. stock futures turned down and stayed lower with the Ohio vote results. (Click here for the latest prices.)
"I'm stunned by the outcome!" said Todd Schoenberger, managing principal at the BlackBay Group, even though some market analysis had suggested that many traders had already priced in an Obama win.
Schoenberger said the market should get a bump in the next few days — simply because there was a definitive outcome to this tight race. "We'll know who we're going to be playing cards with in the next four years," he said.
However, investor Jim Rogers told CNBC: "I will buy more bonds tomorrow, I will buy metals tomorrow. ... Will I buy shares? No."
In the competition for the decisive electoral votes, Obama had 303 to Romney's 206.
In addition to Wisconsin, Paul Ryan's home state, Obama won in Romney's home state of Massachusetts and in Romney's boyhood home of Michigan. But Romney won in Mormon Utah.
Voters also chose a new Congress. Democrats successfully defended their majority in the Senate and Republicans drove toward renewed control of the House as Democrats failed to make any significant inroads into the GOP's delegations from the East, South and Midwest.
In two high-profile Senate races, Democrat Elizabeth Warren, who is considered unfriendly to Wall Street, defeated moderate incumbent Republican Scott Brown in Massachusetts, and Democrat Chris Murphy defeated professional wrestling magnate Linda McMahon in Connecticut. Independent candidate Bernie Sanders was the projected winner for re-election in Vermont, and independent Angus King was projected in Maine for the seat being vacated by Republican Sen. Olympia Snowe.
In Missouri, incumbent Democratic Sen. Claire McCaskill defeated Republican Todd Akin, who had been favored until his controversial comments about rape turned the race around in August. And in the contest to succeed Indiana Republican Sen. Richard Lugar, Tea Party-backed Richard Mourdock, who also was criticized for comments about rape and abortion, lost to Democratic Rep. Joe Donnelly.
Sen. Bill Nelson turned aside a challenge from Republican Connie Mack IV in Florida, and Democrat Timothy Kaine defeated George Allen in Virginia's Senate race.
(Read More: Dems Hold Senate, GOP Keeps House)
Eleven states picked governors, and ballot measures ranging from gay marriage to gambling to union rights were on ballots. Massachusetts voters approved medicinal use of marijuana.
Romney had secured his Republican conservative base in the $2 billion duel for the White House, a race shadowed by a weak economy and high unemployment.
He won in Idaho, Arizona, Montana, Kansas, Louisiana, the Dakotas, Nebraska, Texas, Wyoming, Arkansas, Indiana, Kentucky, West Virginia, Tennessee, Oklahoma, Mississippi, Alabama, Georgia and South Carolina.
In addition to Massachusetts, Michigan and Wisconsin, NBC projected Obama victories in Pennsylvania, New Hampshire, California, Hawaii, Washington state, Missouri, Minnesota, New Mexico, New York, New Jersey, Vermont, Connecticut, Rhode Island, Maryland, Delaware, the District of Columbia, Maine and his home state of Illinois.
The long campaign's cost soared into the billions, much of it spent on negative ads, some harshly so.
In the presidential race, an estimated 1 million commercials aired in nine battleground states where the rival camps agreed the election was most likely to be settled — Ohio, New Hampshire, Virginia, Florida, North Carolina, Wisconsin, Iowa, Colorado and Nevada. They accounted for 110 of the 270 electoral votes needed for victory, and they drew repeated appearances by the 51-year-old president and Romney, 65.
(Read More: The Election and the Great Virginia Divide)
On Election Day, Romney campaigned until the end. He raced to Ohio and Pennsylvania for last-minute campaigning and projected confidence as he flew home to Massachusetts to await the results. "We fought to the very end, and I think that's why we'll be successful," he said, adding that he had finished writing a speech anticipating victory.
Obama made get-out-the-vote calls from a campaign office near his home in Chicago and took to the online site Reddit one more time to ask its members to cast their vote. He also found time for his traditional Election Day basketball game with friends.
(Read More: Obama Uses Reddit to Make Final Plea)
Addressing his rival, Obama said, "I also want to say to Governor Romney, `Congratulations on a spirited campaign.' I know his supporters are just as engaged, just as enthusiastic and working just as hard today." Romney, in turn, congratulated the president for running a "strong campaign."
Other than the battlegrounds, big states were virtually ignored in the final months of the campaign. Romney wrote off New York, Illinois and California, while Obama made no attempt to carry Texas, much of the South or the Rocky Mountain region other than Colorado.
There were 33 Senate seats on the ballot, 23 of them defended by Democrats and the rest by Republicans.
The GOP needed a gain of three for a majority if Romney won, and four if Obama was re-elected. Early projections saw Democrats holding at least 50 seats in the Senate. Neither Majority Leader Harry Reid of Nevada nor GOP leader Mitch McConnell of Kentucky was on the ballot, but each had high stakes in the outcome.
All 435 House seats were on the ballot, including five where one lawmaker ran against another as a result of once-a-decade redistricting to take population shifts into account. Democrats needed to pick up 25 seats to gain the majority they lost two years ago.
The GOP was expected to win about 240 seats, upping its majority by about 10-15 seats.
Speaker John A. Boehner, R-Ohio, raised millions to finance get-out-the-vote operations in states without a robust presidential campaign, New York, Illinois and California among them. His goal was to minimize any losses, or possibly even gain ground, no matter Romney's fate. House Democratic leader Rep. Nancy Pelosi of California campaigned aggressively, as well, and faced an uncertain political future if her party failed to win control.
In a campaign that traversed contested Republican primaries last winter and spring, a pair of political conventions this summer and three presidential debates, Obama, Romney, Vice President Joe Biden and Ryan spoke at hundreds of rallies, were serenaded by Bruce Springsteen and Meat Loaf and washed down hamburgers, pizza, barbecue and burrito bowls.
Obama was elected the first black president in 2008, and four years later, Romney became the first Mormon to appear on a general election ballot. Yet one man's race and the other's religion were never major factors in this year's campaign for the White House, a race dominated from the outset by the economy.
Over and over, Obama said that during his term the nation has begun to recover from the worst recession since the Great Depression. While he conceded progress has been slow, he accused Romney of offering recycled Republican policies that have helped the wealthy and harmed the middle class in the past and would do so again.
(Read More: Will Voters Punish Rich Candidates for Their Wealth?)
Romney countered that a second Obama term could mean a repeat recession in a country where economic growth has been weak and unemployment is worse now than when the president was inaugurated. A wealthy former businessman, he claimed the knowledge and the skills to put in place policies that would make the economy healthy again.
In a race where the two men disagreed often, one of the principal fault lines was over taxes. Obama campaigned for the renewal of income tax cuts set to expire on Dec. 31 at all income levels except above $200,000 for individuals and $250,000 for couples.
Romney said no one's taxes should go up in uncertain economic times. In addition, he proposed a 20 percent cut across the board in income tax rates but said he would end or curtail a variety of tax breaks to make sure federal deficits didn't rise.
(Read More: Where They Stand on Taxes)
The differences over taxes, the economy, Medicare, abortion and more were expressed in intensely negative advertising. (Read More: Where They Stand on Health Care)
Obama launched first, shortly after Romney dispatched his Republican foes in his quest for the party nomination.
One memorable commercial showed Romney singing an off-key rendition of "America The Beautiful." Pictures and signs scrolled by saying that his companies had shipped jobs to Mexico and China, that Massachusetts state jobs had gone to India while he was governor and that he has personal investments in Switzerland, Bermuda and the Cayman Islands.
Romney spent less on advertising than Obama. A collection of outside groups made up the difference, some of them operating under rules that allowed donors to remain anonymous. Most of the ads were of the attack variety. But the Republican National Committee relied on one that had a far softer touch, and seemed aimed at voters who had been drawn to the excitement caused by Obama's first campaign. It referred to a growing national debt and unemployment, then said, "He tried. You tried. It's OK to make a change."
Americans headed into polling places in sleepy hollows, bustling cities and storm-ravaged beach towns deeply divided. More than 30 million voters cast early ballots in nearly three dozen (For states, a reflection of the growing appeal of a relatively new phenomenon.
(Read More: America Votes: Scenes From the Election)
In New York City, scheduled shuttle buses to run every 15 minutes in storm-slammed areas to bring voters to the polls. In Ocean County along the New Jersey coast, officials hired a converted camper to bring mail-in ballots to shelters in Toms River, Pemberton and Burlington Township.
"This is the happiest vote I ever cast in my life," Annette DeBona said as she voted for Romney in Point Pleasant Beach, N.J. The 73-year-old restaurant worker was so worried about not being able to vote that she called the police department several days in advance, as well as her church, to make absolutely sure she knew where to go and when.
(Read More: Storm-Weary Voters Face Long Lines, Confusion)
Renee Kearney, of Point Pleasant Beach, said she felt additional responsibility to vote this Election Day. The 41-year-old project manager for an information technology company planned all along to vote for Obama, but said her resolve was strengthened by his response to Sandy.
"It feels extra important today because you have the opportunity to influence the state of things right now, which is a disaster," Kearney said.
(Read More: Did Chris Christie Cost Mitt Romney the Election?)
Biden and his wife, Jill Biden, were among the first voters Tuesday in at a polling place in Greenville, Del., Biden's home state. Smiling broadly, Biden waited in line with other voters and greeted them with a handshake. Outside he sent a message to people across the country who may encounter crowded polling places. "I encourage you to stand in line as long as you have to," he told television cameras.
The Obamas voted last month in an effort to encourage supporters to vote early. The men on the GOP ticket each voted with their wives at their side Tuesday morning in their hometowns — Romney in Belmont, Mass., and Ryan in Janesville, Wis. — then headed to meet in Cleveland for some retail politicking at restaurants and other unannounced stops. The last-minute nature of the swing made it too difficult to arrange a big public event, but their hope was their joint visit would get local news coverage that might translate to more support.
Romney and Ryan visited a campaign office in Richmond Heights, Ohio, to thank volunteers. "This is a big day for big change," Romney said." The pair then stopped at a nearby Wendy's for quarter-pound hamburgers.
Ten miles to the west, Biden stopped at the Landmark Restaurant lunch counter and apologized for the commotion caused by his entourage. He told diners in one booth he understands they just came to get some spaghetti "and Joe Biden shows up."
Both sides cast the Election Day choice as one with far-reaching repercussions for a nation still recovering from the biggest economic downturn since the Great Depression and at odds over how big a role government should play in solving the country's problems.
"We can make sure that we make even greater progress going forward in putting folks back to work and making sure that they've got decent take-home pay, making sure that they have the health insurance that they need, making sure we're protecting Medicare and Social Security," Obama said in an interview broadcast Tuesday on "The Steve Harvey Morning Show." "All those issues are on the ballot, and so I'm hoping that everybody takes this seriously."
Romney argued that Obama had his chance to help Americans financially and blew it. "If it comes down to economics and jobs, this is an election I should win," Romney told Cleveland station WTAM.