Of course they're doing this. The world just watched them do a genocide and hasn't done anything about it, so of course they feel emboldened to do more vile shit. They are doing whatever they want because there are no repercussions.
Not knowing what how he'd elaborate beyond the confines of the length of a tweet, I'd assume he's talking about lead paint theory. Surely the issue American Republicans extends beyond a single cause like heavy metal poisoning, but I wouldn't automatically think that he's talking about something specifically genetic. There are plenty of other biological causes for changes in a population that don't include genetics. Stuff in the water, environmental contaminants, lax air standards, food additives...we don't know what the long-term effects of some of these things have on people, and studies to identify those problems are probably blocked the same way the effects of smoking were repressed for decades.
Capitalist-focused education systems that reward fitting into boxes over critical thinking wouldn't be considered "biological", but absolutely could be partially blamed for how Americans tend to act. Incentivizing financial success over anything else, including empathy could be partially blamed. Also not biological. Forcing the concept of "rugged individuality" into every aspect of our culture with no concern for community welfare could be partially blamed, and isn't biological. With the festival of different social structures all combining in the process of making an adult in the US, it's no wonder we've got such glaring problems. If you include lax environmental protections, food safety standards, industry lobbying to allow ultra-processed ingredients, sugar subsidies, additives to increase shelf life, those things all do become biological. Hopefully that's what Yugo is talking about.
He probably knows as well as most that with a genetically-diverse country like the US, you could never chalk the issues with conservatism up to something like genes. That still doesn't mean other biological causes aren't factors.
People who are too dumb to realize that they could get paid to astroturf if they thought their time had any value at all?
Amazon gift cards, even?