I’d never think that, of all places, American democracy would be the most volatile
Ignore the political system and look at the economic system. The US is capitalist and as it turns out- capitalism is not mutually exclusive with fascism.
If a human being lives long enough, he will eventually develop cancer. It's simply a natural physical consequence of repeated cell division. Eventually there's some mutation that leads to a chain reaction. The cancer spreads enough and there's no going back. Capitalism, similarly, will always inevitably embrace fascism.
Marx got it wrong. He believed that the workers, realizing their position as class consciousness increases, would inevitably revolt against the power structure. The reality is more depressing.
Capitalism has cycles of crisis. Sometimes the economy is doing good which leaves the workers content. Sometimes the economy is doing bad. The problem is when the economy is doing bad coincides with some other set of crisis, the combination of events radicalizes the workers. This part Marx predicted. However he was mistaken about human nature.
Really, our problem started back in 2008. The global economy never fully recovered. Interest rates were kept low in a desperate attempt to increase spending to keep the boat from tipping. Then COVID pumped up inflation to historic levels- supply chain shortages wrecked chaos. After that, the Russian invasion of Ukraine pushed up inflation even higher. Prices go up but wages lag behind.
Workers, naturally, become more radicalized- as Marx predicted. The issue is Marx was too optimistic about human nature. Humans as a whole are fearful herd animals. They need a shepherd to point somewhere. And eventually, inevitably, some megalomaniac with a vision will take advantage of a vulnerable system and point somewhere. In the 1930s it was to the Jews and the communists. Today, it's the illegals and "wokeism".
All this to say that this shouldn't be surprising. Left wing voices have been warning about this for a long time.