But what about a celebrity who talks to 49 million people a week? Winfrey — who declined requests for an interview — stars in the top-rated daytime talk show in television, publishes a monthly magazine and has a weekly radio show. When she suggested that her viewers read an 800-page Russian classic, as she did in 2004, Anna Karenina became a best seller.
"She's unbelievably influential," says Bill Carroll of Katz Television Group, a programming consultant for TV stations. "Whether she ultimately has political influence or whether she chooses to use that platform is another issue."
After mentioning her support of Obama on CNN last year, Winfrey endorsed him in an interview with Larry King in May. Winfrey has had candidates on her show, but had never endorsed one, she said. "I didn't know anybody well enough to be able to say, 'I believe in this person,' " she said.
In 2004, another superstar jumped into politics: Rocker Bruce Springsteen did a huge get-out-the-vote campaign for Kerry, including a concert in Cleveland days before voters cast ballots. Kerry lost Ohio and the election.
But Winfrey's immense power with audiences means her ability to move voters can't be discounted, strategists say. She "has reach like no one else in the world — to women, which translates to the dinner table and the pillow talk," Reed says. "If she chose to go on the road on a campaign day with Obama, it would be a huge circus."
Winfrey has said she wants to have an influence on Obama's campaign beyond fundraising. "My support of him is probably worth more than any check that I could write," she said on CNN in May. She did write a $2,300 check last month.
Winfrey could host Obama on her show again, write about him in her magazine, make ads and, of course, campaign for him. Obama spokesman Bill Burton says she's promised to be "helpful," but no events have been scheduled.
The TV host's most loyal fans are just the people Obama is fighting to woo away from Clinton. Polls show Clinton has more support from women than Obama does, and Winfrey's audience is largely middle-class women ages 24-54. Winfrey also could help Obama among African-American voters, more of whom favor Clinton in polls even though he is widely viewed as the most viable black contender for president in U.S. history.
Steve Ross, a professor at the University of Southern California who is writing a book about celebrity endorsements, says Winfrey could have a measurable effect. "Her reputation as an activist and a serious, thoughtful person is much greater than any other movie star," he says.
Winfrey's influence also might be great enough to get people who usually don't vote — 36% of the 2004 electorate — to the polls, he says. "There's probably nobody with that potential greater than Oprah," Ross says. If she increased turnout by just 1 percentage point, "1% of an increased vote in key states could swing an election. That's why Oprah's endorsement is different."
Could Winfrey be a nationwide precinct captain, herding voters in the early nominating contests? Obama's opponents, busily wooing Iowa county chairmen, reluctantly concede the point: Oprah is indeed different.
Rasky, Biden's strategist, questions whether a celebrity has what it really takes to win votes. "I'd like to see her going door-to-door in Mason City (Iowa) in January," he says skeptically. "There's no history of celebrity endorsements meaning much. But I'm certainly not going to dismiss Oprah."