For Obama It's the Promised Land - Oprah's Endorsement

Oprah is a brand like no other. Her TV show attracts 8.4 million viewers each afternoon, her magazine has a circulation of 2m and her devotees accept her advice on everything from recipes to what to wear in bed. But can Oprah Winfrey sell a president?

This weekend Winfrey will set a precedent by hosting a political fund raiser at her 42-acre, $50m estate outside Santa Barbara. The recipient of her largesse - Democratic presidential candidate Barack Obama - could see as much as $3m (£1.5m) flow into his campaign as a result.

The event at the Promised Land, the modest name for her mansion, will not be the typical red carpet affair. The great and good - names being bandied about include John Travolta, Will Smith and Halle Berry - will have to park and ride to her mansion and leave their mobile phones behind. But it's not all bad: Stevie Wonder is understood to be among the performers booked for the event.

Obama and Winfrey both hail from Chicago, and are thought to have met during his Senate campaign in 2004. Winfrey announced her support for Obama's candidacy in May. But the fund raiser has spurred rumors that she may take an active role in the campaign, possibly appearing at campaign rallies or on TV commercials. In an interview with CNN's Larry King, Winfrey, the nation's wealthiest African-American, said: "My money isn't going to make any difference. My value to him - my support of him - is probably worth more than any other check that I could write."

Where Winfrey could make a difference for Obama in his efforts to catch up with Hillary Clinton, the Democratic front runner, is with women. Her most loyal viewers are women aged 25 to 55, a demographic that also votes in large numbers in Democratic primaries. During the 2000 campaign George Bush appeared on Oprah at a time when he was struggling in the polls. A week later he had turned a 10% deficit into a 2% lead over the Democratic candidate, Al Gore, a turnaround many attributed to the "Oprah bounce".

But there are questions whether celebrity endorsement can ultimately help or harm a campaign. In 2004 John Kerry had celebrities clustered around him, from Bruce Springsteen to Leonardo DiCaprio. But the most memorable celebrity contribution probably came form Whoopi Goldberg, whose derogatory joke about Bush's name undermined the Kerry campaign.