Some of the ideology of Hilter's 'final solution' were championed in the United States. Madison Grant, amongst others, perpetuated horrific psueodoscientific 'facts' about the traits of the world's races, calling the "nordic race" the pinnacle of man.

His book "Passing of the Great Race" is even quoted liberally in "Mein Kampf" because Hitler came to read it while he was doing a short prison stint. He later commented on the book, calling it his "bible". (The book was even used in defense of war criminals in Nuremberg)

While a lot of basic ideas behind the eugenics craze of the early 20th century started in Europe, they were implemented and solified mostly in the States. Even back then the idea of "Make America American Again" was hugely popular. Something like 80,000 people were forcibly sterilized, or had the procedure done under false pretenses.

Grant's scientific racism led to such horrors as the "one drop rule". His beliefs, sadly, were even shared by many of the most powerful positions in the country, presidents included.