Comedian Chris Rock refuses to be overly vocal in his support for presidential hopeful Barack Obama - in the fear he will ruin the candidate's chances of winning the 2008 election. The comic has joined celebrity supporters Oprah Winfrey and Scarlett Johansson by formerly endorsing the senator - but is afraid his often controversial jokes may keep Obama from reaching the White House. He explains, "You see, I have a mild case of comedic Tourette's. It's so easy for me to say the wrong thing, so I don't want to hurt the guy - 'We coulda had a black President if it wasn't for Chris Rock!' "I think he's a good guy - and I never thought in my lifetime there would be a chance of having a black President."