'Mac is back'
John McCain, his Republican rival, launched a major tour, travelling to seven states in 17 hours including Florida, Virginia, Pennsylvania, Tennessee, Indiana, New Mexico and Nevada before also heading to his home state of Arizona.
McCain, the 72-year-old former prisoner-of-war in Vietnam, has remained defiant.
"There's one day left until we take America in a new direction," McCain told a crowd of about 500 people in Florida earlier in the day.
"The pundits may not know it, and the Democrats may not know it, but the 'Mac is back' and we're going to win this election."
In a break with tradition, both candidates will also be attending events on election day itself.
Obama leads McCain in six of eight key battleground states, including the large states of Florida and Ohio, according to a series of Reuters/Zogby polls released on Monday.
The 47-year-old Obama struck an optimistic tone in an article published in the Wall Street Journal newspaper on Monday, concentrating on the historic nature of his campaign to become the first black US president.
"This is a defining moment in our history," Obama wrote.
"Tomorrow, I ask you to write our nation's next great chapter... If you give me your vote, we won't just win this election - together, we will change this country and change the world."
Obama is holding a one percentage point lead in Missouri and a two-point lead in Florida, according to the Reuters/Zogby polls.
Obama also held leads in Ohio, Virginia and Nevada - all states won by George Bush, the current US president, in 2004.
The five states where Obama is ahead according to the polls have a combined 76 electoral votes.
Taken along with the states won by John Kerry, the defeated Democratic candidate in 2004, Obama would have 328 electoral votes - far more than the 271 votes needed to gain the presidency.
Obama also leads by 11 points in Pennsylvania, which McCain has targeted as his best chance to win-over a state won by the Democrats in 2004.
The Illinois senator also holds a seven-point lead among likely US voters in a separate Reuters/C-SPAN/Zogby national tracking poll, up one percentage point from Sunday.
Under the US political system, the president is elected not by direct popular vote but by capturing 270 out of 538 electoral votes distributed throughout the country in a state-by-state contest.