> what changed?

The algorithms are promoting those views?

Nothing changed - mostly it seems the American condition is a side effect of dedicated partisanship and asymmetric political behavior since the 1970s.

The media apparatus in America has split into a center and left, and then a right wing which has different norms and produces its own products.

That in turn has created a durable political coalition that self referentially calls itself when it needs to support its descriptions on reality.

It’s significantly more effective at producing narratives, and moving ideas from the fringes to the main stream news channels.

Since it has little traffic with the left and center media channels, it avoids counter claims and norms on journalistic standards.

So you can now primary Bipartisan politicians, and then the ideas that gain media attention are the ones that reinforces party talking points. Counter views simply do not get air time.

What we are seeing today, is the progression of those forces, as the narratives are never challenged.

The parent comment didn’t even pose a theory as to why. People can change beliefs over time. Weimar Germany had less Nazis in it than Nazi Germany, which would be equally confusing under your framing.

Material conditions degrading further with no end in sight, a massive influx of money towards right-wing populists appealing to a frustrated middle class, etc. Same story as always. How can a country slide into authoritarianism? It seems impossible until it happens, and by then we can hardly tell we're there.