Rivals Barack Obama and Mitt Romney are approaching the final day of their election battle in a frantic fight for swing state votes.
Each of them spent Sunday addressing crowds across the country, with Mitt Romney speaking in Pennsylvania, a state his aides insist he can now win on Tuesday.
Barack Obama held rallies in New Hampshire and Florida and carried on to Ohio and Colorado in the evening.
Analysts say the election will come down to a handful of swing states.
Barack Obama and Mitt Romney are running almost neck-and-neck in national polls, but polls of many key battlegrounds show Obama narrowly ahead.
However, neither camp is exuding absolute confidence.
The campaign has been most intense in Ohio, which no Republican has ever lost and still made it to the White House.
On Monday morning, Barack Obama is scheduled to appear in Madison, Wisconsin, accompanied by Bruce Springsteen, before going on to Iowa and Ohio.
Mitt Romney is due in Florida – where polls suggest he is ahead – in Virginia, New Hampshire and Ohio.
A final poll published on Sunday by Ohio’s Columbus Dispatch gave Barack Obama a 2% lead – 50% to 48% – over his rival, within the margin of error.
Both candidates visited the Buckeye State on Sunday, with Mitt Romney telling crowds in Cleveland that Barack Obama has failed in his pledge to be a “post-partisan” president and criticizing his record.
“He’s been divisive, blaming, attacking, dividing and – by the way – it’s not only Republicans that he refused to listen to, he also refused to listen to independent voices.”
Later on Sunday he spoke in Morrisville, Pennsylvania, his first visit there in the final stages of the campaign. Democrats say the Romney team’s last-minute decision to campaign in the state is a sign of desperation, but polls do show a tightening race.
“The people of America understand we’re taking back the White House because we’re going to win Pennsylvania,” Mitt Romney told the crowd in Morrisville.
Barack Obama made another appearance in Cincinnati, Ohio, where Stevie Wonder opened a huge evening rally.
Earlier in the day at a rally in Concord, New Hampshire, Barack Obama said: “We have come too far to turn back now.”
He said he would work across party lines to break the political gridlock in Washington, but would not compromise on priorities such as healthcare and college financial aid.
Activists have been stepping up efforts across the crucial swing states.
In Wisconsin, student volunteers have been putting in 14-hour days in an effort to deliver the state for Barack Obama.
An opinion poll on Sunday for ABC News and the Washington Post put the two candidates at 48%, with even voters who term themselves independents split evenly on 46%.
Mitt Romney remains favored among whites, seniors and evangelical Christians; Barack Obama among women, non-whites and young adults.
The president also remains slightly ahead in most of the nine-or-so swing states that will determine the election.
Opinion polls published on Saturday showed him well-placed in Iowa, Nevada and Ohio, but most remain within the polls’ own margins of error.
The election is run using an electoral college. Each state is given a number of votes based on its population. The candidate who wins 270 electoral college votes becomes president.