Why are so many people saying that U.S. Sen. Barack Obama could become the first black president? If by that they mean that he would become the first African-American president -- meaning his father was from Kenya and his mother from Kansas -- it would make sense. But I don't think that's what people mean. Despite the deaths of legal segregation and Jim Crow, apparently most Americans still embrace the one-drop rule. F. James Davis, a retired professor of sociology at Illinois State University, defined the one-drop rule as the belief that any person with ''any known African black ancestry''...