The very first victims of the Holocaust were exactly the same kinds of people targeted in this later American study. They died ten years before the Jews. Their status as a class was codified by the infamous Nuremberg Laws of 1933, which were themselves based on the world's first eugenics legislation, the 1907 Indiana Plan. One thing does indeed lead to another. Such things as Holocausts do not emerge from a historical vacuum.
Nothing emerges from a historical vacuum.
The Holocaust had American roots. This is not the least bit surprising, given America's history. Holocaust is the foundation on which America is built. America is not about freedom and opportunity. The experiments in question were not carried out by nuclear physicists.