I maintain that Nazism had within it the idea of natural selection, lifted from Darwinism.
Hitler may have thought he was employing natural selection, he may have thought he got the idea from Darwin. Hitler wasn't employing natural selection, and had Darwin never mentioned natural selection Hitler would probably still have done what he did.
It was known centuries before Darwin's grandad was a lad that you could breed certain characteristics into animals and people. Agriculture and the domestication of animals proved that beyond doubt. Artificial selection (where man sets the parameters of selection) was a totally accepted phenomena (and indeed where Darwin got his idea from in the first place).
Therefore, Hitler actually used the ancient agricultural methods of selective breeding to the extreme. He realized that there was too much risk that the breeding program would be thrown off course by unwanted specimens breeding with his studs. He couldn't erect a fence to keep his studs isolated from the runts, so he killed the runts so they wouldn't contaminate the gene pool
Hitler may have been inspired by Mendel and selective breeding, but he did not practice natural selection. He created environments where only those he deemed worthy of survival would survive, not environments where those most capable of surviving would survive.
We could argue, that the whole thing was an example of natural selection. Hitler had no children, was violent, sociopathic and genocidal. He got selected against.
Is it a perversion of Darwinism? No, its a perversion of breeding techniques used by farmers, falsely credited to Darwin.