The possible presidential candidacy of the biracial senator has sparked an illuminating debate on race. WE KNOW this: Barack Obama is a rising star. He's a powerful speaker and a gifted writer. He is the only African American serving in the U.S. Senate. But is he black? That's what New York Daily News columnist Stanley Crouch asked last month, and his answer was decidedly "no." No, Crouch wasn't just employing the old "blacker than thou" canard. Nor was he concerned with the fact that Obama was raised by his white mother. Rather, he was treating blackness not just as a...