Michelle Obama (center) and Oprah Winfrey listen as Barack Obama addresses the crowd during the rally at the Columbia, S.C., football stadium. The crowd was the election campaign's biggest yet. (AP photo by Gerry Broome / December 9, 2007)
Democratic presidential candidate Sen. Barack Obama, with wife Michelle (left) and talk show host Oprah Winfrey, greet supporters at a campaign rally at Williams-Brice Stadium in Columbia, S.C. Organizers said more than 29,000 attended the event on the second day of the Obama-Winfrey tour of early-voting states. (AP photo by Mary Ann Chastain / December 9, 2007)
Obama raises a microphone to catch the crowd's roar during the Columbia rally. (AP photo by Gerry Broome / December 9, 2007)
Michelle Obama (left) and Oprah Winfrey do a high-five while Democratic presidential hopeful Barack Obama addresses the crowd at Williams-Brice Stadium. (AP photo by Mary Ann Chastain / December 9, 2007)
Sen. Barack Obama hugs wife Michelle to Oprah Winfrey's approval during the Democratic presidential contender's campaign event in Columbia, S.C. (AP photo by Mary Ann Chastain / December 9, 2007)
After the rally, some of the estimated 29,000 people who attended wave farewell to the Obamas and Oprah Winfrey from the stadium in Columbia, S.C. (Getty photo by Stephen Morton / December 9, 2007)
Talk show host Oprah Winfrey looks on as Democratic presidential candidate Sen. Barack Obama addresses a crowd of more than 18,000 in Des Moines on Saturday, Dec. 8. (Tribune photo by José M. Osorio / December 8, 2007)
Sen. Barack Obama hugs Oprah Winfrey at the beginning of a campaign appearance in Des Moines on Saturday. It was Winfrey's debut on the presidential campaign trail. (Tribune photo by José M. Osorio / December 8, 2007)
Democratic presidential candidate Sen. Barack Obama chats with some of the crowd at a campaign rally in Des Moines on Saturday. (Tribune photo by José M. Osorio / December 8, 2007)
Crowd members wave campaign signs as Oprah Winfrey leaves the stage after a rally for presidential candidate Sen. Barack Obama in Des Moines on Saturday. (Tribune photo by José M. Osorio / December 8, 2007)
Sen Barack Obama speaks to the crowd at a campaign rally in Des Moines on Saturday as his wife Michelle (center) and talk show host Oprah Winfrey listen. (Tribune photo by José M. Osorio / December 8, 2007)
A huge American flag is the backdrop as Sen. Barack Obama takes the stage for a campaign rally in Des Moines on Saturday. (Tribune photo by José M. Osorio / December 8, 2007)
Spectators greet presidential candidate Sen. Barack Obama with a large sign at a campaign rally in Des Moines on Saturday. (Tribune photo by José M. Osorio / December 8, 2007)
Oprah Winfrey walks onto the stage after being introduced by Michelle Obama at a campaign rally for Sen. Barack Obama on Saturday. "I am not here to tell you what to think," Winfrey said. "I am here to ask you to think." (Tribune photo by José M. Osorio / December 8, 2007)