On a day that began for Hillary Clinton with a ham and cheese omelette in a cramped diner, Barack Obama is standing in a vast arena, his arm around Oprah Winfrey, who has just told 18,500 cheering Democrats: “I am here to tell you, Iowa: he is the one!”

Winfrey, a woman so powerful that one favourable word can turn a product into a sales blockbuster – her praise for Anna Karenina sent it straight to the top of the bestseller list – has just delivered perhaps the first pivotal celebrity endorsement in presidential politics to the largest crowd in Iowa caucus history. It is not meant to be like this in the Hawkeye State, where they like to size up their politicians in living rooms and school libraries, without live rock bands and a billionaire talk-show diva who hopes to do for Mr Obama in his campaign what she did for Leo Tolstoy.

“It’s time for us to dream America anew again and support Barack Obama,” the First Lady of television declared, as cable TV news programmes cut live to the event and camera flashes filled the huge hall in central Des Moines. “That is why for the very first time in my life I feel compelled to stand up and speak out for the man who I believe has a new vision for America. We need Barack Obama.”

Kicking off a two-day tour with Mr Obama through the crucial early nominating states of Iowa, New Hampshire and South Carolina, Winfrey, who has never endorsed a politician before, is giving Mr Obama an incalculable boost by delivering him vast crowds in the closing days of the campaign.

A further 10,000 Iowans filled a venue in Cedar Rapids on Saturday night, before another free-ticket rally in an 80,000-seat football stadium in South Carolina yesterday. In Manchester, New Hampshire, all 12,000 tickets were gone for their appearance last night, the biggest primary campaign event in the Granite State’s history.

In a hastily arranged effort to blunt the Winfrey appeal, Mrs Clinton campaigned in Iowa on Saturday with two last-minute celebrity guests of her own: her daughter, Chelsea, 27, and her mother, Dorothy Rodham, 88, who shuns publicity. Her last interview was in 2004 – on the Oprah Winfrey Show.

Mrs Clinton also dispatched her husband, Bill, to campaign in South Carolina, the day before the Obama-Oprah bandwagon rolled into the Palmetto State. In the past three weeks, she has almost doubled her Iowa staff, to 220.

Mr Obama is a candidate suddenly on a roll, and for the first time within his campaign there is a genuine belief that he can beat Mrs Clinton. In recent polls, he has opened a small lead over the former First Lady in Iowa, has reduced her once-formidable lead in New Hampshire to single digits and has virtually wiped out her advantage in South Carolina. Voters in all three states believe that Mrs Clinton is better qualified to be President, but even more say that they want a fresh start.

Celebrity endorsements rarely produce results in presidential contests, but with Winfrey, an almost ecumenical political figure, America is entering uncharted waters. She is admired across every demographic. Nearly nine million people watch her show daily. After she announced that she would campaign for Mr Obama, the Clinton team rolled out the endorsement of Barbra Streisand. It was a puzzling move to many. In Winfrey, 53, Mr Obama has an exemplar of the nonpartisan, postBush, post-baby-boomer politics of change that is his core message. Americans trust her judgment. In the veteran liberal Streisand Mrs Clinton has an uncomfortable reminder merely of the way we were, as the singer’s anthem puts it.

In a clear reference to Mrs Clinton, and her vote authorising the Iraq war – a conflict that Mr Obama opposed from the outset – Winfrey said: “I am so tired of politics as usual.” She added: “The amount of time you spend in Washington means nothing unless you are accountable for the judgment you made.” Mr Obama, she said, “stood with clarity and conviction against this war in Iraq”.

To win the nomination Mr Obama must attract women and African-American voters away from Mrs Clinton and in Winfrey he has a powerful messenger. Three quarters of her viewers are women. More than half of those are over 50; 44 per cent earn less than $40,000 (£20,000) a year. These fit the profile of Mrs Clinton’s core women supporters. And Mr Obama is making significant inroads. In South Carolina, half the Democratic primary electorate is African-American, a key base of Winfrey’s fans. Mr Obama has wiped out Mrs Clinton’s lead among this group in the South. In New Hampshire, more women from blue-collar households support him than Mrs Clinton.

Whether Winfrey’s endorsement will deliver votes is uncertain. But Iowans such as Norma Reed are the campaign’s hope. She arrived at the event because she loves Winfrey, but is a firm supporter of John Edwards, the other main challenger in the state. Afterwards she said: “That was very compelling. Obama was very persuasive. I might have just changed my mind.”

From farm girl to chat-show queen

- Born in Kosciusko, Mississippi, in 1954 and raised on a pig farm until aged 6 by her paternal grandmother

- Aged 19 she became the youngest person and the first African-American woman to anchor the news, at WTVF-TV, in Nashville

- She moved to Chicago in 1984 and became a talk-show host. The Oprah Winfrey Show started in 1985

- The show is watched by 46 million viewers a week in America and has been the country’s most popular talk show for 21 consecutive years

- The show has featured 1,115,100 audience members over 20 years, with women outnumbering men 19:1

- She is the only person to have appeared five times in Time magazine’s annual list of the 100 most influential people in the world

- The 2007 Forbes Rich List placed Winfrey as the 165th-richest person in America, with a net worth of $2.5 billion (£1.3 billion), making her the richest self-made woman in the US

- She gives $50 million a year to charitable causes to help women, children and families

Sources: museum.tv; oprah.com; forbes.com; businessweek.com; Business Week

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