The tightly fought race for the White House headed into its final hours as the candidates jetted around the country making closing arguments Sunday about the economy, the auto bailout and gridlock in Washington.
President Barack Obama, 51, a Democrat, and Republican challenger Mitt Romney, 65, are separated in national polls by a fraction of a percentage point.
They crossed paths Sunday in Ohio, the ultimate prize among the seven main swing states.
In addition, Obama visited New Hampshire, Florida and Colorado on Sunday, while Romney fly to stops in Iowa, Virginia and Pennsylvania.
A Wall Street Journal poll on Sunday gave Obama a 1-per-cent lead in a national poll, 48 to 47 per cent, but that latest data had not been factored into the average of polls compiled on the Real Clear Politics website, which still gave Obama a 0.2-per-cent lead.
Armies of volunteers for both parties were blanketing the battleground states, contacting likely supporters to confirm they would vote and offer transportation to polling stations.
Closing arguments in Ohio focus on Obama's 2009 bailout of Chrysler and General Motors.
Romney, a former governor of Massachusetts, had condemned the bailout at the time, saying the industry should be allowed to go bankrupt - a statement that has come back to haunt him, particularly in industry-heavy Ohio.
At a rally Friday in Springfield, Ohio, Obama told supporters who booed when he mentioned Romney's name that "voting is the best revenge." During his own rally Sunday in Cleveland, Romney took issue with Obama's comment.
"Instead, I ask the American people to vote for love of country," Romney said. "We've got to lead America to a better place together, and we will. We're two days away from a fresh start."
Obama is seeking re-election with unemployment at 7.9 per cent. No president since World War II has won a second term with unemployment above 7.2 per cent.
Growth for 2012 is still below 2 per cent, but Obama has sought to remind voters of the crisis in which he was elected four years ago.
"Remember, in 2008, we were in the middle of the worst economic crisis since the Great Depression. We were in the middle of two wars," he said Sunday at a high school in Hollywood, Florida.
"And today, our businesses have created nearly 5.5 million new jobs. The auto industry is back on top. Home values are beginning to rise again. We're less dependent on foreign oil than at any time in the last 20 years.
"The war in Iraq is over. The war in Afghanistan is coming to a close. Al-Qaeda is on the run - Osama bin Laden is dead."
An estimated 27 million people have already cast ballots in early voting. More than 130 million Americans voted in the 2008 presidential elections.
Voters will decide all 435 seats in the House of Representatives, expected to remain majority Republican, and one-third of the 100-member Senate, expected to keep a narrow Democratic majority.
The election takes place as the north-east US recovers from Hurricane Sandy, which destroyed thousands of homes, killed more than 100 people in the US alone and shut down power, public transport and fuel delivery for millions of people, especially in hard-hit New Jersey and New York.
Obama has maintained a slight advantage in the battleground states. The presidency is not decided by the national popular vote, but rather by a system of electoral votes assigned to each state based on their population-based representation in Congress. To capture the White House, a candidate needs 270 votes, which nearly every state awards on a winner-take-all basis.
Obama looks to have a firm hold of 243 votes in heavily Democratic states, while Romney can claim 206, putting more pressure on him to win more of the swing states.
Campaign lawyers are preparing for long counts in the closest swing states.
Some experts anticipate prolonged court fights similar to those in 2000, which took five weeks to award the White House to George W Bush, who won with a 537-vote advantage in Florida out of 6 million votes cast.
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