The abandoning of evidence and data happened long before Trump. Denying evolution, denying climate change, promoting abstinence only education, etc. Look to Liberty University if you want to see what a Republican institute of “higher learning” looks like.
White supremacists like to claim that twin studies prove that black people are less intelligent due to genetics. Apparently Sam seems to think that Democrats refusing to accept the shoddy science behind twin studies (the conclusions of which are often used in service of racist meta-studies) somehow implies that they are also "anti-science". Probably best to just ignore the comment.
Twin studies are mostly used to show that traits are heritable at an individual level.
Edit: It strikes me that the strawman argument you've constructed is a perfect example of left-wing science denial. The endemic use of the technique in fields like psychology, criminology, biology, is something you prefer to ignore.
Yup. "Scientific" racism has a long history. Some of the various Confederate declarations of secession claim natural inferiority as a cause for slaveholding.