President Obama has four campaign stops scheduled. On Sunday morning, he headed to New Hampshire, where former president Bill Clinton joined him at a rally in Concord. Obama will later travel to Florida, Ohio and Colorado.
Clinton joked at the New Hampshire rally that there's a "rampant virus" going around called "Romnesia," explaining that when Romney predicted the economy would produce 12 million jobs over four years if he won, he forgot to mention a Moody's Analytics forecast released in August before that promise, saying the U.S. will gain that number of jobs "if we just don't mess with what the president has already done."
Obama's campaign is mobilizing a massive get-out-the-vote effort, while the former governor of Massachusetts makes a late play for votes in Democratic-leaning Pennsylvania.
"I think the effort probably is more to inspire voters to get out and vote rather than to try to persuade them as to the campaign argument this late in the game," CBC's Washington correspondent Keith Boag said.
The Democrats have a million-voter registration advantage in Pennsylvania. Obama senior adviser David Plouffe said that means Romney would have to win two-thirds of the state's independents, a prospect he called "an impossibility."
Romney will be in Pennsylvania on Sunday, as well as Iowa, Ohio and Virginia.
Ohio is especially important for Romney because no Republican has ever won the presidency without capturing that state.
Romney's visit to Morrisville, Pa., 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.
The tally for spending on the 2012 election could reach $5.8 billion, up 7.8 per cent form the 2008 election, and $1.2 billion more than the international community pledged to help rebuld Haiti after the 2010 earthquake.
Much of that spending comes from so-called "Super PACs," or political action committees, independent groups that can raise unlimited funds from undisclosed donors. Super PACs became legal as a result of a U.S. Supreme Court decision in 2010.
National opinion polls show a race for the popular vote so close that only a statistically insignificant point or two separated the two rivals.
Polls in the nine battleground states tightened after Obama's poor performance in the first presidential debate, on Oct. 3, and the race has stayed too-close-to-call since then.
Americans have been casting ballots in early voting for a couple of weeks now, with a turnout estimated at 27 million. No votes will be counted until Tuesday.