Steve Ross, chairman of the University of Southern California's history department, said the ongoing use of celebrities during the White House fight between U.S. Sens. Barack Obama, D-Ill., and John McCain, R-Ariz., is vital for their electoral efforts, ABC News reported Thursday.

"The two things you need to win are money and people's attention and celebrities can get you a little of both," Ross said.

Hollywood star George Clooney threw his celebrity weight behind the Democratic Party candidate for president with an appearance Tuesday in Switzerland. His is among notable names such as talk show host Oprah Winfrey and actor Ben Affleck to back Obama.

McCain been backed in his presidential run by celebrities such as Kelsey Grammer, Sylvester Stallone and Jon Voight.

Center for Responsive Politics spokesman Massie Ritsch told ABC News celebrities' fame, not money, is what the politicians need the most.

"If anything," he said, "they are probably most valuable to a campaign as headliners for fundraising events that bring in more donors."