Obama was closing out the campaign with an apparent edge in some key battleground states, including Ohio. But both campaigns were predicting wins in Tuesday's election.
Romney's campaign was projecting momentum and banking on late-breaking voters to propel him to victory in the exceedingly close race. His political director, Rich Beeson, suggested Sunday that Romney could earn more than 300 electoral votes on Election Day. He needs just 270 to win.
Making his closing case to voters Sunday in Des Moines, Iowa, Romney pledged, if elected, to work with Democrats to restore the American dream and bring the economy roaring back to life.
"We're Americans. We can do anything," Romney said. "The only thing that stands between us and some of the best years we can imagine is a lack of leadership - and that's why we have elections."
Obama, too, said he is willing to work across party lines to break Washington's gridlock, but assured some 14,000 supporters who gathered in Concord, N.H., he would not compromise key Democratic priorities such as health care and college financial aid.
"I know I look a little bit older, but I've got a lot of fight left in me," Obama said. "We have come too far to turn back now. We have come too far to let our hearts grow faint. It's time to keep pushing forward."
Bridging the partisan divide could be easier said than done for both candidates. Obama has faced hard-nosed opposition from House Republicans during his first term. Senate Majority Leader Harry Reid, D-Nev., has said it's "laughable" for Romney to think Senate Democrats will help pass his agenda.
Romney was cutting away briefly Sunday from the nine or so competitive states that have dominated the candidates' travel itineraries. Romney, along with running mate Paul Ryan, had an early evening event planned in Morrisville, Pa., his first rally in the state this fall.
Romney's visit follows the decision by his campaign and its Republican allies to put millions of dollars in television advertising in Pennsylvania during the race's final weeks. Obama's team followed suit, making a late advertising buy of its own.
"You saw the differences when President Obama and I were side-to-side in our debates," Romney says in a new TV ad filmed at an Ohio rally and released Sunday. "He says it has to be this way. I say it can't stay this way. He's offering excuses. I've got a plan. I can't wait for us to get started."
The campaign did not say where the ad would run.
The Republican ticket cast the late push into Pennsylvania as a sign that Romney had momentum and a chance to pull away states that Obama's campaign assumed it would win handily. The president's team called the move a "Hail Mary" and a sign Romney still doesn't have a clear pathway to reaching 270 Electoral College votes. Democrats have a million-voter registration advantage in Pennsylvania.
"This is a desperate ploy at the end of a campaign," said David Plouffe, a top adviser to Obama's campaign, on ABC's "This Week," arguing that Romney would have to win 2 out of 3 independents to pick up Pennsylvania. "He's not going to do that anywhere, much less Pennsylvania."
The two vice presidential candidates both planned hectic days of campaigning that had them crisscrossing the map. Ryan made a quick stop outside the Green Bay Packers' stadium in his home state of Wisconsin. Donning a Packers jacket and a yellow and green striped tie, Ryan and his family dropped by a tailgating party before setting off for Ohio, Colorado and Minnesota.
Vice President Joe Biden, campaigning in Cleveland suburb of Lakewood, told a crowd of about 1,200 people that Romney and Ryan were trying to fool voters by claiming to be more moderate than they really are.
"These guys are trying to play a con game here at the end," Biden said.
But no one was working harder than the two men at the top of the ticket. In addition to Pennsylvania and Iowa, Romney planned events Sunday in Ohio and Virginia.
Obama had a full schedule, with campaign stops Sunday in New Hampshire, Florida, Ohio and Colorado. He caught a few hours of sleep back at the White House Saturday night before hitting the campaign trail again Sunday. When Marine One lifted off from the South Lawn Sunday morning, it was the last time Obama would see the executive mansion until after Election Day.
Even as he dashed from campaign stop to campaign stop, Obama was careful to avoid the perception he had taken his eye off recovery efforts from Hurricane Sandy. As Obama flew Sunday from Washington to New Hampshire, White House spokesman Jay Carney said the president was getting regular updates and would have a full briefing from top officials, including Homeland Security Secretary Janet Napolitano, who is in New Jersey on Sunday to view storm damage.
Former President Bill Clinton, who has joined Obama on the trail for the waning days of the race, called Obama's handling of the storm a clear example that the president has the right approach to fixing the nation's messes.
"It was a stunning example of 'we're all in this together' is a way better philosophy than 'you're on your own,'" Clinton said as he introduced Obama in Concord.
Both candidates were drawing large crowds as they dropped in and out of the most competitive states. Obama and Clinton drew 24,000 people to an outdoor rally in Bristow, Va., on a cold Saturday night. Romney's Friday night rally in Ohio drew more than 20,000 people.
The president's rallies are aimed at boosting Democratic enthusiasm and motivating as many supporters as possible to cast their votes, either in the final hours of early voting or on Tuesday, Election Day. Persuading undecided voters, now just a tiny sliver of the electorate in battleground states, has become a secondary priority.
Obama's campaign said it had registered 1.8 million voters in key battleground states, nearly double the number of voters they registered in 2008. Campaign officials said volunteers had made 125 million personal phone calls or door knocks with voters.