In return for their $2,300 (£1,133) admission fee, guests were forced to leave their cars in a car park eight miles away and climb on board buses, told they must wear flat shoes to protect the “sacred” lawns, then stripped of their mobile phones and cameras.

But such is the drawing power of Oprah Winfrey and Barack Obama that there was little complaint when the queen of daytime TV hosted a $3 million (£1.5 million) fundraiser for her prince. About 1,500 guests were allowed to set their flat-soled feet on the grounds of Ms Winfrey’s 42-acre estate in Montecito, near Santa Barbara, California, on Saturday evening. Inside they dined on mini-hamburgers, chicken and corn on the cob while sitting on Obama-embroidered blankets.

Most of the donors — despite paying the maximum amount allowed under law to Mr Obama’s presidential campaign — were denied access to a VIP reception and dinner. They will have had at best only a fleeting handshake with these iconic black Americans, as well as the chance of spotting celebrities such as Sidney Poitier, Tyler Perry and Stevie Wonder.

Ms Winfrey even warned guests to be on their best behaviour after being invited to her “special, sacred, spiritual” $50 million mansion.

George Bush’s revival in 2000 after languishing up to ten points behind Al Gore in the polls was attributed widely to the “Oprah bounce” of an appearance on her show. But now she says that Mr Obama is the only presidential candidate she will showcase.

Admitting that she never expected to be endorsing a presidential campaign, she added: “When you have been called, no one can stand in the way of destiny.” Her involvement could even extend to appearing on the campaign stump with Mr Obama or making TV adverts backing him. “My money isn’t going to make any difference. My support of him is probably worth more than any cheque that I could write,” she said recently.

For Mr Obama there are also risks. Appearing alongside such a huge star could lead to him being outshone, while reinforcing a criticism that his campaign has a little too much glitter and not enough weight.

According to a recent Gallup poll, Ms Winfrey is considered the second-most-influential woman in the US. The only trouble is that occupying first place is Mr Obama’s main rival for the Democratic presidential nomination: Hillary Clinton.

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