What koenkai says about people with somewhat misfortune crypto-eugenicist beliefs often congregating in certain leftist circles in this country is entirely correct, more's the pity, although I note that the one of these types (albeit only regarding a specific mental state, not abnormal mental states in general) currently running for Senate is a Republican.
Crypto-eugenicist beliefs tend to harp on "improving the species" by twisting Darwinism into...something else entirely. So it's really hard to get a crypto-eugeniscism through a party where much of the base rejects that entirely.
IIRC, eugenics in America was always popular among two types: progressive reformer WASP types from California/NY and racists who wanted to sterilize blacks. But I would think that the former group is far more ascendent today, since the explosion of evangelical Christianity in the South probably shredded eugenicist thought there. Regardless, these groups have a long history in the USA.
I also suspect it's a Protestant thing. Since the only other countries to engage in huge amounts of eugenics were the Scandinavian countries, where it was a bipartisan effort (both the conservatives and social democrats approved). Then again, that might be going way too far. Scandinavian eugenics was pretty terrifying.
Japan also had a brief resurgence in Eugenics after World War II, though it was interestingly pushed by the JSP and then later shut down after the reverse course and ascendance of the LDP.
