A black slave is torn apart by dogs as a crowd of white overseers savors the sight and a black bounty hunter watches passively behind shades. A black father makes his little girl crack open a crab with her bare hands then flex her tiny muscles like a pint-size N.F.L. linebacker. A black pilot snorts a line of cocaine after a night of debauchery and, just a few minutes before liftoff, knocks back several miniature bottles of alcohol. A black woman tells President Lincoln that God will guide him as he pushes legislation that will end slavery but not dent notions of white supremacy.