After a long, bitter and expensive campaign, national polls show Obama and Romney are essentially deadlocked ahead of Tuesday's election, although Obama has a slight advantage in the eight or nine battleground states that will decide the winner.
Obama plans to visit three of those swing states on Monday and Romney will travel to four to plead for support in a fierce White House campaign that focused primarily on the lagging economy but at times turned intensely personal.
The election's outcome will impact a variety of domestic and foreign policy issues, from the looming "fiscal cliff" of spending cuts and tax increases that could kick in at the end of the year to questions about how to handle illegal immigration or the thorny challenge of Iran's nuclear ambitions.
The balance of power in Congress also will be at stake on Tuesday, with Obama's Democrats now expected to narrowly hold their Senate majority and Romney's Republicans favored to retain control of the House of Representatives.
In a race where the two candidates and their party allies raised a combined $2 billion, the most in U.S. history, both sides have pounded the heavily contested battleground states with an unprecedented barrage of ads.
The close margins in state and national polls suggested the possibility of a cliffhanger that could be decided by which side has the best turnout operation and gets its voters to the polls.
In the final days, both Obama and Romney focused on firing up core supporters and wooing the last few undecided voters in battleground states.
Romney reached out to dissatisfied Obama supporters from 2008, calling himself the candidate of change and ridiculing Obama's failure to live up to his campaign promises. "He promised to do so very much but frankly he fell so very short," Romney said at a rally in Cleveland, Ohio, on Sunday.
Obama, citing improving economic reports on the pace of hiring, argued in the final stretch that he has made progress in turning around the economy but needed a second White House term to finish the job. "This is a choice between two different versions of America," Obama said in Cincinnati, Ohio.
FINAL SWING-STATE BLITZES
Obama will close his campaign on Monday with a final blitz across Wisconsin, Ohio and Iowa - three Midwestern states that, barring surprises elsewhere, would be enough to get him more than the 270 electoral votes needed for victory.
Polls show Obama has slim leads in all three. His final stop on Monday night will be in Iowa, the state that propelled him on the path to the White House in 2008 with a victory in its first-in-the nation caucus.
Romney will visit his must-win states of Florida and Virginia - where polls show he is slightly ahead or tied - along with Ohio before concluding in New Hampshire, where he launched his presidential run last year.
The only state scheduled to get a last-day visit from both candidates is Ohio, the most critical of the remaining battlegrounds - particularly for Romney.
The former Massachusetts governor has few paths to victory if he cannot win in Ohio, where Obama has kept a small but steady lead in polls for months.
Obama has been buoyed in Ohio by his support for a federal bailout of the auto industry, where one in every eight jobs is tied to car manufacturing, and by a strong state economy with an unemployment rate lower than the 7.9 percent national rate.
That has undercut Romney's frequent criticism of Obama's economic leadership, which has focused on the persistently high jobless rate and what Romney calls Obama's big spending efforts to expand government power.
Romney, who would be the first Mormon president, has centered his campaign pitch on his own experience as a business leader at a private equity fund and said it made him uniquely suited to create jobs.
Obama's campaign fired back with ads criticizing Romney's experience and portraying the multimillionaire as out of touch with everyday Americans.
Obama and allies said Romney's firm, Bain Capital, plundered companies and eliminated jobs to maximize profits. They also made an issue of Romney's refusal to release more than two years of personal tax returns.