Wary of voter overconfidence Obama not letting up

US: "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," the Democratic presidential nominee told supporters Thursday.

"Not now. Not now," Obama said in the Florida sunshine. "We've got to work hard." 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.

In his race against Republican John McCain, Obama has gone big, drawing hundreds of thousands of people to rallies in the last 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 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 grilled him at length about his environmental record. One said she wanted tickets to his inauguration. One made him smile by saying she was 100 percent Obama. "I won't let you down," he told her.

Despite all the polling pointing in his favor, there remains a feeling in his campaign that anything can happen at the end. Obama appears easy and unworried - he even took time Thursday to visit a pumpkin patch - but signs and words of overconfidence are shunned.

COLOMBIA, Missouri, Friday, AP