CEDAR RAPIDS, Iowa — Oprah Winfrey had just come through freezing rain and blowing snow — glamorously dressed, of course, in a lavender velvet jacket and shiny black heels. As she stepped onto the stage of the vast indoor arena, dozens of television cameras rolled; flashbulbs popped; and the crowd roared. But in the down-home way that has arguably made her the most accessible superstar in America, Winfrey quickly kicked her celebrity status down a notch with a self-effacing quip.

"As we were slipping and sliding on the highway, I said, 'Nobody is going to be there,' " deadpanned Winfrey, her hair coiffed into loose ringlets, her eye makeup just so. " 'Nobody is going to be there, 'cause I know where I would be: home in my pajamas, with my footsies on!' "

The crowd exploded with laughter; more flashbulbs lit up around Winfrey, and the U.S. Cellular Center trembled with deafening applause.

It was a signature moment for the queen of talk, whose empire is built on her uncanny ability to connect with an audience, the knack for giving regular folks the feeling that — despite her estimated net worth of $2.5 billion — she is one of us.

Winfrey made her first foray on the campaign trail last weekend, lending her celebrity-appeal to U.S. Sen. Barack Obama in a swing through Iowa, New Hampshire and South Carolina, and drawing a total of 70,000 people, some of whom wore buttons that read "Oprah for VP" and waved signs that read "Oprah + Obama (heart)."

But not every Oprah fan is overjoyed about the star's leap into the political fray. Some believe her appearances could backfire, alienating viewers and angering fans.

Already, daytime devotees have lashed out on Oprah.com message boards. "OPRAH IS A TRAITOR!!!!" screamed one message. "In bad taste," declared another. "I will never watch your show again," wrote a third.

Indeed, Winfrey's step into the often-bitter world of partisan politics is a risky move for a woman who has carefully crafted her image to appeal to a broad and diverse audience. With shows about "favorite things," and her "angel network," Winfrey has long been a uniter — a woman who has transcended race, class and political divides — and brought women together with feel-good, mass-appeal slogans such as "Live your best life!" Now, her endorsement has shaken her fan base and threatened to splinter her viewership along partisan lines.

Some irate fans argue that Winfrey should continue her longtime support of women by endorsing U.S. Sen. Hillary Clinton.

Others contend the talk-show host should remain nonpartisan. "If Oprah was going to be fair about all this, wouldn't it be great if she had the top three candidates from each party on her show?" said Karen Zmoos, 49, a Cedar Rapids homemaker who supports Mitt Romney. "I feel like she is trying to sway her mass following. It's like telling us that Obama is the only one."

CELEBRITY IMPACT

Entertainment executives have long discouraged celebrities from speaking about politics. "The moment a star opens their mouth and endorses one candidate, they alienate half their viewership," said Steve Ross, a professor at the University of Southern California who is writing a book about celebrity endorsements.

Charlie Chaplin, Jane Fonda and the band the Dixie Chicks are on the long list of entertainers who have ventured onto political terrain and afterward suffered the wrath of furious fans. "Stars are part of our fantasy world," Ross said. "And when our fantasy figures step off the stage and begin to preach politics, it's like throwing a cold towel over our faces."

What's more, celebrity endorsements generally have little impact. Bruce Springsteen and Michael Jordan endorsed candidates in recent presidential elections; Springsteen gave his nod to John Kerry in 2004, and Jordan filmed a commercial for Bill Bradley in 2000. But neither endorsement made a difference, experts said. And neither politician made it to the White House.

Some believe that Winfrey — with her near ubiquitous presence in today's media landscape and her golden touch when it comes to product endorsement — could be different. According to a recent study by the Pew Research Center, Winfrey is more influential than most celebrities, ranking on par with Bill Gates and slightly behind Alan Greenspan. And though nearly 70 percent of people said Winfrey would not influence their vote, about 60 percent believe that she will help Obama's candidacy.

POSITIVE TOPICS

Winfrey has long focused her show on positive topics, steering clear of partisanship and controversy. It is a strategy that began in earnest in 1994, when Winfrey resolved to remake herself as the feel-good host of the daytime shows, said Janice Peck, an associate professor at the University of Colorado at Boulder and author of the upcoming book "The Age of Oprah." "It was a conscious decision to separate herself from the trash pack."

In the following years, Winfrey introduced uplifting shows with topics such as "How to live your dreams," "Love letters to your parents" and "Random acts of kindness." Such inspirational themes proved wildly popular, and Winfrey quickly leveraged that appeal to launch a media empire, including her book club, her magazine and programs on XM Satellite Radio.

Winfrey's influence, in many ways, has transcended race, culture and class. She is most popular among white women older than 55, who make up 40 percent of her audience. Of her 7.6 million daily viewers, 78 percent are white and 18 percent are black, according to Nielsen Media Research. But Peck notes, "The way she transcends race is to appeal to a majority white audience by being black culturally but not being black politically."

That has changed with her endorsement of Obama, who would be the first African-American president in the U.S.

"Oprah is someone who is obviously black," said Todd Boyd, a professor at the University of Southern California who studies race and culture. "Now here she is endorsing a black candidate. Some of her fans might say, 'Finally.' Others might say, 'I didn't see her in that way before. Now she's endorsing her candidate, and it's solely based on race. This is different than the Oprah I know.' "

GENDER POLITICS

Gender politics provide another potential pitfall, with some fans feeling disappointed that Winfrey, with her long history of advocating for women, isn't endorsing Clinton.

"Oprah has been for women all along," said Marlene Mentzer, 63, a retired nurse who was sitting in her car in Cedar Rapids on a bitter cold day and preparing to canvass a local neighborhood for the Clinton campaign. "I just don't get it. Her endorsement of Obama seems like a contradiction."

In speeches and interviews, Winfrey has acknowledged the gamble. "This is stepping out of the box. I've never taken this kind of risk before," she told a rapt audience in Cedar Rapids. In an interview with The Hollywood Reporter in November, she said: "I weighed that: What is the cost to me for doing it? Am I going to lose viewers?"

If the endorsement is a risk, it is one she is willing to take.

Winfrey has previously said that she would leave her show in 2011, meaning that the 2008 race will be the last presidential election under her reign. "A second-term president starts thinking about their place in history, and I think that is what Oprah is beginning to think about," said Melissa Harris-Lacewell, an associate professor at Princeton University who studies race and politics.

"If Obama becomes the first black president, then she was on the right side of history."

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