Barack Obama has launched an eight-state, 40-hour "campaign marathon extravaganza" to protect his narrow lead in the key battlegrounds that will decide a knife-edge election.
With just 13 days to go before he asks voters for a second term, Obama's through-the-night, coast-to-coast trip was to take in six of the most contested swing states in his battle against Republican challenger Mitt Romney.
Supporters of Romney, who was on a similar odyssey, are talking up what they claim is their new momentum in the closing stages of the race and both are striving to exude confidence.
"We're going to pull an all nighter," Obama told a cheering crowd at his first rally under a steel grey sky and yellowing trees in Davenport, Iowa, the state where he began his unlikely quest for the presidency in 2007.
"This is where it all began four years ago, on your front porches, in your backyards - this is where the movement for change began."
As Obama set off for Iowa, Colorado, Nevada, Florida, Virginia and Ohio, his campaign spokeswoman Jen Psaki dismissed talk from Romney's camp of "secret momentum", insisting the president was leading or tied in all the key states.
She also branded Romney untrustworthy, accusing him of disguising "extremely conservative" positions on health policy and foreign affairs. "He has been untruthful about his positions with the American people," she said.
Obama, who has a well appointed cabin in the nose of Air Force One, was to sleep on a red-eye flight from Las Vegas to Tampa later on Wednesday.
On board, he will take the opportunity of time on flights criss-crossing the country to call undecided voters and campaign workers, drumming up the vote ahead of the November 6 election.
He will also divert from swing states to safe Democratic territory during his tour to tape an appearance on the Tonight Show with Jay Leno in Burbank, California and cast an early vote in his hometown, Chicago.
The trip --mocked as the Can't Afford Four More tour by Romney's campaign - comes with Obama tied or just behind Romney in national polls, but still with small leads in a handful of the swing states.
If the election were held today and polls are accurate, Obama would win around 280 electoral college votes in the state-by-state race, 10 more than he needs to return to the White House for four more years.
But Romney's camp believes it has momentum after he won the first of the rivals' debates in October, and avoided serious missteps in the other two, in which Obama was seen as the stronger performer.
Romney, while taking shots at the president over his trip, had problems of his own on Wednesday, as he sought to distance himself from controversial remarks on rape made by a fellow Republican.
Anti-abortion Senate candidate Richard Mourdock's statement that pregnancy caused by rape was "something God intended to happen" gave Obama a new opening to attack his rival's record on women's rights.
With the presidential candidates locked in a virtual tie, women voters in swing states could decide the election, and a fresh row over abortion would distract from Romney's focus on the sluggish US economy.
Speaking at a Senate debate late on Tuesday, Mourdock said he believed life begins at conception and opposed abortion in all cases except when the mother's life was in danger.
"I struggled with it myself for a long time, but I came to realise life is that gift from God, and I think even when life begins in that horrible situation of rape, that it is something that God intended to happen," he said.
Romney's campaign moved to distance him from the remarks, with spokeswoman Andrea Saul saying "Governor Romney disagrees with Richard Mourdock's comments, and they do not reflect his views."
But the Obama campaign sensed a new chance to brand Romney as uncaring about women and their health choices.
"The President felt those comments were outrageous and demeaning to women," Psaki said.
Romney has said he opposes abortion, a signature issue for many evangelicals and social conservatives in the Republican base vote, except in cases of rape or incest, or to save the mother's life.