Election battle shifts to Florida
Mr Obama has warned against complacency
The rivals for the White House are starting to focus on the key Southern states won by George Bush in 2004, with just 18 days to go before the vote.
John McCain, who is trailing in the opinion polls, must hold Virginia, North Carolina and Florida to have a realistic chance of being elected.
Meanwhile, the Obama campaign is pouring resources into Florida, a state once seen as leaning Republican.
Mr McCain will be in Florida on Friday, while Mr Obama arrives on Monday.
Senator McCain will hold a rally in Miami, hoping to mobilise his support among Cuban-Americans, while Senator Obama will campaign in Tampa before joining Hillary Clinton for a rally in Orlando, on the first day that postal voting opens in Florida.
There was some assumption that Florida was going to be fairly solid on our side
Florida Republican Party chairman Jim Greer
Mr McCain is also planning on drawing on the help of Senator Joe Lieberman, who is popular with Jewish voters in the state. The latest opinion poll in Florida, for CNN, puts Obama at 51% and McCain on 46%.
Mr Obama, who will stop first in Virginia, is showing his confidence by campaigning at the weekend in two states that were not widely considered close until recently - Missouri and North Carolina - before heading further south.
The Democrats have begun running ads in West Virginia for the first time, while the Republican National Committee has pulled its ads in Wisconsin, one of the mid-western states Mr McCain once hoped to win.
This week the Obama campaign has sent some of its key organisers to Florida, including deputy campaign director Steve Hildebrand.
In January Mr McCain's victory in the Florida primary boosted his campaign
The Democrats are also reportedly ready to spend $40m on television advertising - and have already outspent the McCain campaign five to one in the key media markets of Tampa, Orlando and Miami.
"You're going to see lots of Barack Obama, Michelle Obama, Joe Biden and Jill Biden on the ground in Florida," Obama Latino campaign director Temo Figueroa told Bloomberg News. "If we win Florida, Barack Obama is president. There's no way for John McCain to win without Florida."
A key advisor to the McCain campaign, Steve Schmidt, acknowledged on NPR radio that the Republicans would be in trouble if they did not win Ohio and Florida.
"The fact that we're in the race at all, within striking distance with a 5% right track, is a miracle. Because the environment is so bad and the headwind is so strong," he added.
The Republicans are planning to hire paid canvassers to help get out their vote - which is particularly among Cuban-Americans and retired military voters - in order to counter the strong grassroots organisation of the Democrats.
"There was some assumption that Florida was going to be fairly solid on their side and maybe they didn't anticipate this being as close," Florida Republican Party chairman Jim Greer told the Miami Herald, commenting on the McCain campaign.
Warning on complacency
Meanwhile, Mr Obama is warning his supporters against complacency.
Mr Obama maintained his lead in the final debate
"For those who are getting a little cocky, I've got two words for you: New Hampshire. I learned right here that you can't let up or pay too much attention to the polls," he told his supporters at a rally in Londonderry, New Hampshire on Thursday.
Senator Obama received the endorsement of the Washington Post, which said that "the choice is made easy in part by Mr McCain's disappointing campaign."
"It is made easy in larger part, though, because of our admiration for Mr Obama and the impressive qualities he has shown during this long race," it added.