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This photo combo made from file photos shows President Barack Obama, left, and actor George Clooney. Obama says Clooney is a good friend and a good person who is sensitive about protecting that friendship. The president tells Entertainment Tonight in an interview airing Monday, Aug. 20, 2012 that he got to know Clooney through his work on Sudan when Obama was in the U.S. Senate. (AP Photo)

Celebrity endorsements

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