Democrat Barack Obama and Republican John McCain raced through the battleground states of Ohio and Pennsylvania on Sunday, with McCain struggling to overtake Obama's lead in the final 48 hours of a gruelling White House campaign.
Obama warned supporters against overconfidence during rallies in Ohio, one of about a dozen crucial battleground states that will decide Tuesday's election to succeed unpopular President George W. Bush.
The Illinois senator leads McCain in national opinion polls and in many key Republican-leaning states as a two-year campaign that has cost more than $2 billion (1.2 billion pounds) draws to a close.
"Don't believe for a second that this election is over," Obama told a crowd of more than 60,000 in Columbus. Another 80,000 greeted him in Cleveland, where rocker Bruce Springsteen warmed up the audience and introduced Obama.
"We can't afford to slow down, sit back, or let up for one day, one minute, or one second in these last few days," said Obama, who would be the first black U.S. president.
McCain reached out to undecided voters in Pennsylvania, his best and perhaps last hope of stealing a Democratic-leaning state from Obama as the two candidates search for the 270 electoral votes needed for victory.
He also visited Peterborough, New Hampshire, another state won by Democrats in 2004 and where he scored key wins in 2000 and earlier this year in the primary.
The Arizona senator is battling to overcome a strong challenge from Obama in about a dozen states won by Bush in 2004, and he and his top aides said he was closing the gap at the end.