DEPRESSING episodes in American race relations come and go, but this one may stick.  As we write, the news of the verdict in the O.J. Simpson trial is still fresh, though a new drama has quickly replaced the original one. Race—not crime and punishment—is its theme.  And, while the long-running show that ended on the third of October was part soap, part sporting event (with an array of television pundits keeping score), this one is no fun at all. Unforgettable images have flitted across our television screen: of cheers, hugs, and high fives among black crowds; of racist graffiti in Brentwood, the white, traditionally liberal, upscale neighborhood in which O.J. and Nicole both lived. Are we two nations or one? The question—long a staple in the rhetoric of the left—must now be taken seriously.