In Cedar Rapids, fans packed the chilly concert arena, clutching signs that read "Change we can believe in" and "Obama '08." Barbara Elam, 71, a retired banker, had volunteered to work the campaign phones three times a week to snag "priority" tickets that allowed her access to ground-floor seats in the 9,500-capacity concert hall. On Saturday, she brought along her friend Imelda Collins, 55, a medical transcriptionist. Collins said she had decided long ago to support Obama.
"He's honest and he's for the people," she said.
Collins said she was heartened by Winfrey's support. "Since she endorsed him, that made me even more confident in my decision," she said.
Despite the formidable competition for attention, Clinton also campaigned in Des Moines on Saturday.
"The citizens of Iowa will understand that they would be much happier to have Hillary Clinton talking to President Bill Clinton . . . in the White House than Barack Obama getting his advice from a TV salesperson," said Keith Uhl, 61, a Des Moines lawyer who appeared on stage with Clinton.
But thousands of Iowans at the Obama event disagreed.
"You want Oprah as vice president?" Obama asked to loud cheers from the audience.
For Winfrey, a guardian of the brand of her behemoth multimedia company, the telegenic Obama with his inspirational politics is a neat fit. For Obama -- well, who doesn't want the support of someone Forbes magazine has named the world's most powerful celebrity?
"This is like being endorsed by Walter Cronkite," said Joel Aberbach, a professor and founding director of the UCLA Center for American Politics and Public Policy, who added that the two have similar inspirational messages.
"If I had to pick a nonpolitical character to endorse me, it's hard for me to think of anyone I would rather have on my side," agreed Matthew Baum, a visiting associate professor of public policy at the John F. Kennedy School of Government at Harvard University. "It's not just star power," he said. "What she has is an enormous reservoir of credibility and trust with . . . exactly the people Obama needs to reach out to."
Former Iowa Gov. Tom Vilsack, a Clinton supporter, tried to downplay the importance of Winfrey's endorsement recently, telling the Washington Times that women in Iowa are too busy working to watch Winfrey's show.
But the ratings tell a different story. Her show attracts an average of 40,000 viewers each weekday, according to Nielsen Media Research.
"At the end of the day, an endorsement is just an endorsement, and she's not going to single-handedly deliver the nomination to him -- no endorsement has that kind of power -- but what we've seen is that Obama's campaign has been rejuvenated," Baum said. "These giant rallies could really help with the momentum and make a difference by challenging the narrative about Clinton as the anointed candidate."
The Oprah and Obama show goes on the road today in South Carolina and New Hampshire.
Times staff writers Scott Martelle and Peter Nicholas in Des Moines contributed to this report.