In Philip K. Dick’s 1962 alternative-history novel “The Man in the High Castle,” a single, terrifyingly plausible shift in history has produced a profoundly transformed world. In 1933, Franklin Delano Roosevelt is assassinated at a rally in Florida, setting off a chain of disastrous events: after Republicans take power and reverse the New Deal, the U.S. neither recovers from the Great Depression nor enters the Second World War.