Polling stations opened across the eastern United States and Midwest, with the West Coast soon to follow, as Election Day dawned. At least 120 million people were expected to render judgment on whether to give Obama a second term or replace him with Romney.
Their decision will set the country's course for the next four years on spending, taxes, healthcare and foreign policy challenges like the rise of China and Iran's nuclear ambitions.
National opinion polls show Obama and Romney in a virtual dead heat, although the Democratic incumbent has a slight advantage in several vital swing states - most notably Ohio - that could give him the 270 electoral votes needed to win the state-by-state contest.
Romney, the multimillionaire former head of a private equity fund, would be the first Mormon president and one of the wealthiest Americans to occupy the White House. Obama, the first black president, is vying to be the first Democrat to win a second term since Bill Clinton in 1996.
Whichever candidate wins, a razor-thin margin would not bode well for the clear mandate needed to break the partisan gridlock in Washington.
Romney voted at a community center near his home in a Boston suburb before dashing off for two last-minute stops, including the most critical of all swing states - Ohio.
"I feel great about Ohio," he said when asked about what is considered a must-win for him.
Obama, settled into his home town of Chicago, made a final pitch to morning commuters with pre-recorded interviews broadcast in battleground states.
"Four years ago, we had incredible turnout," Obama told a Miami radio station. "I know people were excited and energized about the prospect of making history but we have to preserve the gains we've made and keep moving forward."
Fueled by record spending on negative ads, the battle between the two men was focused primarily on the lagging economic recovery and persistent high unemployment, but at times it turned personal.
After months of campaigning and billions of dollars spent in the battle for leadership of the world's most powerful country, Obama and Romney were in a virtual nationwide tie ahead of Tuesday's election, an overt symptom of the vast partisan divide separating Americans in the early years of the 21st century.
Obama appeared to have a slight edge, however, in some of the key swing states such as Ohio that do not vote reliably Democratic or Republican. That gives him an easier path to reach the 270 electoral votes needed to win the presidency.
Romney decided to make a late dash to Cleveland and Pittsburgh for rallies on Tuesday before returning to his Boston home to await the returns. Obama, who spent Monday night at his home on Chicago's South Side, opted to make a dozen radio and satellite TV interviews from Chicago to swing states to keep his closing arguments fresh in voters' minds.
Romney has made a late-campaign drive for Pennsylvania, a state that had been seen as solidly in the Obama column. The move was widely seen as a push - perhaps against all odds--to compensate for Obama's expected victory in Ohio.
A combination photo shows Mitt Romney speaking in Indianapois, Indiana, and Barack Obama at a campaign rally in Mentor, Ohio. AFP
Under the US system, the winner of the presidential election is not determined by the nationwide popular vote but in state-by-state contests. The candidate who wins a state - with Maine and Nebraska the exceptions - is awarded all of that state's electoral votes, which are apportioned based on representation in Congress.
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
"It's a choice between two different visions for America," Obama declared Monday in Madison, Wisconsin, asking voters to let him complete work on the economic turnaround that began in his first term. "It's a choice between returning to the top-down policies that crashed our economy, or a future that's built on providing opportunity to everybody and growing a strong middle class."
Romney argued that Obama had his chance and blew it.
"The president thinks more government is the answer," he said in Sanford, Florida. "No, Mr. President, more jobs, that's the answer for America."
It wasn't just the presidency at stake Tuesday: All 435 seats in the House of Representatives, a third of the 100 Senate seats, and 11 governorships were on the line, along with state ballot proposals on topics ranging from gay marriage to legalizing marijuana. Democrats were expected to maintain their majority in the Senate, with Republicans doing likewise in the House, raising the prospect of continued partisan wrangling no matter who might be president.
The two candidates and their running mates--Vice President Joe Biden and Republican Rep. Paul Ryan--stormed through eight battleground states and logged more than 6,000 flight miles (9,600 flight kilometers) Monday on their final full day of campaigning.
US President Barack Obama and first lady Michelle Obama walk off Air Force One after arriving at O'Hare International Airport in Chicago. AP
Obama's final campaign rally, Monday night in Des Moines, Iowa, was filled with nostalgia as he returned to the state which launched him on the road to the White House in 2008 with a victory in its lead-off caucuses over Hillary Rodham Clinton, now his secretary of state. A single tear streamed down Obama's face during his remarks, though it was hard to tell whether it was from emotion or the bitter cold. The president had campaigned earlier in the day in Wisconsin and Iowa.
Profile of US President Barack Obama
Obama, making his last run for office at the still-young age of 51, was tickled to have rocker Bruce Springsteen along as his traveling campaign, telling the crowd in Madison, "I get to fly around with him on the last day that I will ever campaign - so that's not a bad way to end things." The president urged voters in Iowa to help him finish what they started here four years ago. "I've come back to Iowa one more time to ask for your vote," Obama told 20,000 supporters at the outdoor rally. "This is where our movement for change began."
After rallies in Florida, Virginia and Ohio, Romney returned Monday night to New Hampshire, where he won the state's first-in-the-nation primary in January, speaking to about 10,000 people at the Verizon Wireless arena.
Romney, 65, assailed Obama's economic policies amid the recession, and promised to bring change that he asserted Obama had only talked about.Profile of Mitt Romney
"Talk is cheap, but a record is real," Romney said. If elected, Romney would be the first Mormon U.S. president.
The final Washington Post-ABC News tracking poll, released Monday, showed Obama with support from 50 percent of likely voters to 47 percent for Romney. The poll had a margin of error of 2.5 percentage points.
Fitting for a tight election, voters in tiny Dixville Notch, New Hampshire, split over the candidates, Obama and Romney receiving five votes each when balloting took place at midnight. In nearby Hart's Location, the hamlet that shares the traditional honor of casting the first presidential ballots on Election Day, Obama won with 23 votes, Romney received nine and Libertarian Gary Johnson received one.
Supporters wave signs during a rally for Republican presidential candidate Mitt Romney at the Verizon Wireless Arena in Manchester, New Hampshire. AFP
More than 30 million absentee or early ballots have already been cast, including in excess of 3 million in Florida.
Obama and Romney, a former Massachusetts governor and the ultra-wealthy founder of a private equity firm, have spent months highlighting their sharp divisions over the role of government in Americans' lives, in bringing down the stubbornly high unemployment rate, reducing the $1 trillion-plus federal budget deficit and reducing a national debt that has crept above $16 trillion.
The economy has proven a huge drag on Obama's candidacy as he fought to turn it around after the near financial meltdown and deepest recession since the Great Depression of the 1930s, a downturn that was well under way when he replaced George W. Bush in the White House on Jan. 20, 2009.
Obama insists there is no way reduce the staggering debt and safeguard crucial social programs without asking the wealthy to pay their "fair share" in taxes. Romney, who claims his successful business background gives him the expertise to manage the economy, favors lowering taxes and easing regulations on businesses, saying this would spur job growth.
In surveys of the battleground states, Obama held small advantages in Nevada, Ohio, Iowa and Wisconsin - enough to deliver a second term if they held up, but not so significant that they could withstand an Election Day surge by Romney supporters. Romney appears to be performing slightly better than Obama or has pulled even in North Carolina, Virginia and Florida.
The biggest focus has been on Ohio, an industrial state that has gone with the winner of the last 12 presidential elections, which both candidates visited Monday. No Republican has ever won the White House without carrying Ohio.
Both campaigns say the winner will be determined by which campaign is better at getting its supporters to the polls. The president needs the overwhelming support of blacks and Hispanics to counter Romney's big lead among white males.
Romney, who described himself as "severely conservative" during the Republican primary campaign, has shifted sharply in recent weeks to appeal to the political center, highlighting his claim to have been deeply bipartisan when he was governor of Democratic-leaning Massachusetts.
The forecast for Election Day promised dry weather for much of the country, with rain expected in two battlegrounds, Florida and Wisconsin. But the closing days of the campaign played out against ongoing recovery efforts after Superstorm Sandy. Election officials in New York and New Jersey were scrambling to marshal generators, move voting locations, shuttle storm victims to polling places and take other steps to ensure everyone who wanted to vote could do so.
(With inputs from Reuters, AP)
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