“Every door out… is a door in.” In season 4, episode 2, Dr Mengele and his portal experiments return. The program has advanced significantly in the last year, with regular teams of Nazi spies making the trip to the Alt-World for both espionage and sabotage. Thanks to Hawthorne Abendsen and the Reich’s enhanced interrogation methods, Mengele has also made a map of the multiverse. John Smith understands the potential waiting for them in each world- if the Nazis can send someone to a new world, that world can send someone to the High Castle world as well. Everyplace is a potential threat.
Including schools and homes in the American Reich, since children have been taught to spy on and turn in their loved ones. Some, like Amy, are very enthusiastic about enforcing the rules. Jennifer isn’t happy about being back in the Reich, so John has to play referee between his two daughters to keep them both alive.