Thousands of Iowans have flocked to his office, and have 1,385 signed up as volunteers to score tickets to see the talk show diva and magazine queen. The campaign declines to say how many tickets have been distributed for two events Saturday in Iowa but says no one will be turned away from the unique opportunity to attract new voters.

After all, Obama is engaged in a tight, three-way race with Hillary Rodham Clinton and John Edwards and the Jan. 3 caucuses are less than four weeks away.

Obama entered the Democratic presidential race with a significant disadvantage, a newcomer in national politics running against one of the world's most famous women in Clinton. Winfrey gives him his own female star power to help draw voters. The campaign hopes the "O factor" can sell the candidate the way it does books or products featured on her show.

"The only other universally adored person coming to Iowa this December is Santa," said Obama's Iowa press secretary Tommy Vietor.

Winfrey has never backed a political candidate before, but on behalf of her Chicago hometown senator is making the two stops in Iowa Saturday - in Des Moines and Cedar Rapids - before heading Sunday to South Carolina and New Hampshire with Obama and his wife. The campaign moved the biggest event to the 80,000-seat University of South Carolina football stadium after running out of the 18,000 tickets originally available.

In Iowa, Winfrey's show wins its time slot overwhelmingly in the state's four largest media markets - Des Moines, Cedar Rapids, Davenport and Sioux City. KCCI, the Des Moines station, has the 12th highest viewership in the country for the show.

Obama adviser Steve Hildebrand said two-thirds of those in South Carolina who snapped up the first batch of tickets were voters who had never been identified by the campaign before.

"We'll use this as an opportunity to begin a dialogue with them," Hildebrand said. "We expect this to be powerful, but we don't know it for sure because it hasn't been done before by her. Even if this has a small amount of influence, it's going to matter."

Any Iowan can get tickets by signing up online or visiting one of Obama's 37 statewide offices. At the state headquarters in Des Moines, 22-year-old field assistant Prianka Sharma has spent the week distributing blue priority tickets and white general admission from a table set up in the entrance.