Mr Romney has a narrow lead in recent national tracking polls.
Yesterday Mr Obama predicted he would reach agreement to cut the US deficit and reform immigration law within his first year if elected to a second term.
On immigration, the Democratic Party incumbent said that if he wins a second term, “a big reason” will be because Republicans have “so alienated the fastest-growing demographic group, the Latino community”.
Mr Obama is hammering Mr Romney over his shift to the centre after months campaigning as a hard-right conservative.
Mr Romney, looking to sustain momentum that grew out of his victory in the first presidential TV debate three weeks ago, is bashing Mr Obama as a leader who has failed to bring the economy back to full speed.
Both men are making huge efforts to sway the small pool of undecided voters, while imploring their millions of supporters to vote, particularly in key battleground states such as Ohio and Iowa, where early voting is already under way.
Mr Obama planned a short stop in Chicago today to cast his own vote – the first time an incumbent has voted early.
The election map has shrunk to no more than nine of the 50 US states, and that is where both candidates will be spending virtually all of their time in the final days before the 6 November election. Residents in those battleground states do not reliably vote either Republican or Democrat. The president is chosen according to state-by-state contests, not the popular vote.
Mr Obama was planning to cover 5,300 miles yesterday in the most-travelled single day of his re-election bid. He was going from Washington to Iowa, Colorado, California and Nevada, and then overnight to Florida – the first time he was spending the night flying on Air Force One for a domestic trip. Mr Obama will break for an appearance on the widely watched The Tonight Show with Jay Leno and make calls to voters from the plane.
Mr Romney, too, was picking up the pace yesterday, campaigning in Nevada and Iowa before a three-stop tour of Ohio today. He told a crowd of 10,000 supporters Mr Obama’s promise of more of the same is “why he’s slipping and we’re gaining”. Mr Obama’s campaign insisted the president was holding on to a slight lead in most of the nine battleground states – Nevada, Colorado, Iowa, Wisconsin, Ohio, Virginia, North Carolina, Florida and New Hampshire
“We have the ball, we have the lead,” his campaign strategist David Axelrod insisted.