It's a hot take, but: Social Media.

The algorithms are beyond destructive, they're actively malicious. You are fed a constant diet of affirming (in a general, not TRA, sense) content, things that agree with your worldview, posts, and are tailored to your very specific (and even personal) demographic. Slowly, fringe views no longer seem fringe because you see them all the time, and newer and newer fringe views seep in, and the cycle repeats.

I've seen numerous people on both left and right succumb to this and this is the unifying thing. They are terminally online, they get all their information from Twitter/Facebook/Instagram/YouTube, they're always sharing memes (feeding the algorithm), and once it's taken hold it just builds on itself. It doesn't matter what the content is: Qanon MAGA shit, trans shit, or hell even gardening shit. It happens the same way regardless.

Couple this with the fact that huge swaths of my (millenial) and younger generations have built basically their entire social lives online. For the zoomers, in a lot of cases it literally is their only social live, even among their IRL peers. This is also why cancel culture is so effective; the idea of having your whole social life destroyed for making one false move makes everyone anxious and hyper-reflexive in their affirmations of loyalty to the cult ("TWAW", "the election was rigged", etc.).

I don't know if there's even a way to fix this, short of massive deprogramming on a societal level. But since this serves the ruling class, and the majority have seemingly succumb to it, I don't know how to even begin fighting back, at least not in their realm. Only IRL can help.

Finally I think the timing with the end of the (second) Obama term was mostly coincidental. This really started very early in the 2010's with the rise of the algorithms on Facebook, Twitter, and YouTube, which was then adopted by other social media sites/apps. It really started to show itself in 2016 after a gradual initial climb, and has now become almost all-encompassing.