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Illinois Senator and Democratic presidential candidate Barack Obama speaks during the 'Generation Obama' concert at the Gibson Theatre in Universal City, California, 10 December 2007. Polls show a tightening race between Obama and New York Senator Hillary Clinton. AFP PHOTO GABRIEL BOUYS (Photo credit should read GABRIEL BOUYS/AFP/Getty Images)

Illinois Senator and Democratic presidential candidate Barack Obama speaks during the 'Generation Obama' concert at the Gibson Theatre in Universal City, California, 10 December 2007. Polls show a tightening race between Obama and New York Senator Hillary Clinton. AFP PHOTO GABRIEL BOUYS (Photo credit should read GABRIEL BOUYS/AFP/Getty Images)