Obama: We won't sit back or let up

Columbia: "Here I am, signed, sealed, delivered." That's what the giddy crowds at Barack Obama's campaign rallies hear when he walks off the stage, the booming sound of Stevie Wonder singing about the promise of a sure thing.

The curious part is that Obama keeps saying just the opposite: Not one thing is sealed.

"We can't afford to slow down, or sit back, or let up, for one day, for one minute, for one second in this last week," he told supporters on Thursday. "Not now. Not now. We've got to work hard," Obama said in the Florida sunshine.

For a range of reasons - the slippery nature of polls, the Democrats' history of heartbreak, the still-to-be-determined effect of race, the desire not to jinx himself - Obama is, in fact, working the vote hard.

The Democrat was to break for a Halloween visit to his two young daughters in Chicago before heading to an evening rally in Highland, Indiana, just over the Illinois border.

In his race against Republican John McCain, Obama has gone big, drawing hundreds of thousands of people to rallies in the past few days alone.

He used his fundraising muscle to buy a prime-time TV slot for his infomercial, viewed by 33.6 million, and touted his new unity with former president Bill Clinton.

But Obama also is careful to look engaged individually, too. Twice this week, in campaign offices outside Denver and in Pittsburgh, he got on the phone directly with voters.

One woman made him smile by saying she was 100 per cent Obama.

"I won't let you down," he told her.