- May 2014
To my knowledge, the issue of eugenics wasn't actually directly raised in the Congressional debates over immigration restrictionism in the 1920s. However, it was raised elsewhere in the US during this time:You mentioned eugenics in your post.
In the US, The influence of this belief can clearly be demonstrated in the Immigration Act of 1924 which severely reduced Asian immigration and immigration from Southern and Eastern Europe. Refer to the Wikipedia article for that law and you will see a pretty comprehensive description.
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So, it's possible that US Congressmen and Senators knew about this issue and related the issue of eugenics to immigration restrictionism, but apparently they weren't actually willing to openly and publicly say this--else it would have appeared in the Congressional debates over immigration restrictionism during this time.