By Rajesh Mirchandani
BBC News, Columbia, South Carolina
With less than a month until the first stage of voting for the US presidential candidates, some big name celebrities have been out on the campaign trail.
One of the biggest - Oprah Winfrey - spoke at a series of rallies this weekend for Democratic hopeful Barack Obama.
But can famous friends really make a difference?
The first people in line at Williams-Brice Stadium in Columbia, South Carolina, arrived before 0600.
By midday the queue was 100m long and several people wide. It looked to be at least 80% African-American, probably three-quarters female.
Many had dressed up in their church best, a little hot under their starched collars in temperatures of 70F plus (21C).
Inside, local bands were warming up the crowd and it felt more like a rock concert than a political rally.
This may have been an event for Democratic presidential hopeful Barack Obama, senator for Illinois, but the candidate was sharing the limelight.
Many people had been drawn by the presence of Oprah, not Obama
"I have to say, I'm here to see Oprah," a middle-aged African-American woman told me.
Further back in the queue, a younger black woman said: "For me it's 50-50. I like Oprah but I also like Obama."
The man she was with was less hesitant: "For me it's Oprah. I'm interested to hear Obama also. They might have dragged me out of bed for him, but Oprah got me here willingly."
Such is the pulling power of the Oprah Winfrey, queen of TV talk shows. Her weekly audience is estimated at some 50 million and she is reckoned to be the highest-paid entertainer in America.
About 29,000 people came to the Columbia rally - thought to be the largest event for any candidate in this election campaign. The organisers had to switch to a bigger venue.
That's the "Oprah Effect".
She was introduced on stage by Barack Obama's wife, Michelle, as "the first lady of television", and came on to huge, prolonged, spine-tingling cheers.
But then, this was her TV audience flocking to see her in the flesh, dominated by African-American women: the type of voters Barack Obama needs to win over.
And Ms Winfrey did her best to do that for him.
She talked passionately and eloquently about his opposition to the war in Iraq, his concern for the poor and how he had an "ear for eloquence and a tongue dipped in the unvarnished truth".
On the campaign trail in Iowa the day before, Ms Winfrey had told the crowd: "I'm not here to tell you what to think, I'm here to ask you to think."
At times it felt hard to tell the difference, when her endorsement of him was so comprehensive and resounding.
It is possible, although quite unlikely, that some people may vote for Mr Obama because their favourite TV star, Oprah Winfrey, says she will. After all, a recent poll suggested she is the second most influential woman in America.
But far more likely is that she will bring more people to hear what Mr Obama has to say.
As he puts it: "Oprah is beloved across the country... ultimately, though, I'm going to need to make the sale for people to support me."
This may prove especially hard given that the person who topped the poll of America's most influential women was his main rival for the Democratic nomination: Hillary Clinton.
Hillary Clinton has her own celebrity backers - notably husband Bill
She, too, has her celebrity backers, not least her husband Bill (during his last term as president the average African-American family's wage went up by more than white families' and that is one reason why the Clintons remain hugely popular among black voters).
Superstar singer Barbra Streisand has come out in support of her too and, at a recent fundraising event in Washington DC, Mrs Clinton thanked "my friend and one of the really wonderful writers in America today, John Grisham" for introducing her on stage.
But many experts believe few celebrities can compete with the Oprah Effect.
Eleanor Clift, from Newsweek magazine, says: "It's hard for me to think that Barbra Streisand coming out for Hillary would make that much difference to the vote totals... [but] Oprah has a proven track record.
"If you can get on her show with a book, you have got a bestseller, so she knows how to move product."
But does she know how to move voters? It is only weeks until the first states vote for their preferred candidates in the primaries, among them South Carolina on 29 January.
In what may be a tight race, if the Oprah Effect can translate into even a few votes, it could make all the difference.