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FILE - in this Dec. 9, 2008 file photo, then-Democratic presidential hopeful, Sen. Barack Obama,D-Ill., with his wife Michelle, left, and talk-show diva Oprah Winfrey, right, take part in a campaign rally in Columbia, S.C. The president's re-election campaign is increasingly sounding like a nostalgia tour. His speeches stroll through elections past, serving up fond memories of his days running as a political unknown, identifying early political inspirations and reminding voters that, win or lose, this will be his last campaign after 13 appearances on the ballot since 1996. (AP Photo/Mary Ann Chastain, File)

FILE - in this Dec. 9, 2008 file photo, then-Democratic presidential hopeful, Sen. Barack Obama,D-Ill., with his wife Michelle, left, and talk-show diva Oprah Winfrey, right, take part in a campaign rally in Columbia, S.C. The president's re-election campaign is increasingly sounding like a nostalgia tour. His speeches stroll through elections past, serving up fond memories of his days running as a political unknown, identifying early political inspirations and reminding voters that, win or lose, this will be his last campaign after 13 appearances on the ballot since 1996. (AP Photo/Mary Ann Chastain, File)

Celebrity endorsements

Help or hindrance, Hollywood stars have been putting their weight behind politicians for decades.