I really wouldn't discount social media, which he has shown an addiction to.

I've personally watched a very close friend go from a huge Obama / liberal supporter to supporting Trump, Canada's trump mini, full on climate change denial, anti vaccine stuff by going down the right wing conspiracy theory rabbit hole. All on twitter/youtube/facebook etc stuff. He doesn't watch MSM.

There's definitely a rich/yes man aspect as well, but social media echo chambers can have a huge influence.

edit: and for what it's worth, it's not worth trying to reason with him anymore, and the relationship has pretty much died during covid.