That's likely an artifact of the circles you run in. If you're on HN, then odds are really good you don't mill around in the lower socio-economic milieu many of the "foot soldiers" of radical movements draw upon, whichever part of the political spectrum we're discussing. Our very vocabulary distinguishes us as a separate "other"; when I speak with them, I have to consciously "tune into" their preferred vocabularies.

The financial bifurcation in the US and to a lesser extent in many other parts of the developed world is quite big, and I don't know how big it has to get before a competent demagogue gets traction in the US. The extremes in both the GOP and the DNC have just been handed a dangerous working template with Trump's history lesson. They just learned that extremism works, and it scales from local to national politics. It was not always so; one of the salient features of American politics in the past was just how consistently difficult it was to move the center any appreciable distance politically, the infamous "lumpentariat".

I believe this is because the US valuation landscape is fundamentally broken. This goes way beyond the economic or financial system. How we account for value over time is structured in very perverse incentive structures leading to the power law popping up in an all-over fashion when in the past it didn't use to dominate the landscape so much (it had localized instantiations but these were more local maxima than a general law more widely applicable). It's generating a "desperation deciles" that the means and averages of metrics sweep under statistical rugs.

I think these deciles are mattering now due to the law of large numbers. With "only" a 100M population base, such deciles are manageable, whether through coercion (unfavorable), assistance (nominal approach), or generationally long-term rehabilitative policy like public education (ideal). But I suspect there is something about near-billion- and billion-scale population governance our governing systems are not scaling to meet.

Also, a consistent theme I see in these kinds of discussions is similar to your "...if the people who were truly destitute and down-trodden could find some way to ignore the superficial partisanship that they've been sold and unite under social and economic policy...". In my humble and limited experience, the ones in the developed world are short-term focused on survival, putting food on the table and a roof over their heads, then with what limited discretionary time and cognitive energy left over, trying to find some happiness in a pretty bleak outlook as globalism systemically blocks their avenues of escape.

There are some limited avenues left, but the arithmetic doesn't support lifting enough of the desperation deciles out of poverty or functional poverty to matter through transitioning them to plumbers, welders, fitters, rig work, etc. While there are currently screaming needs for many of those skills, it isn't in the tens of millions scale we're needing (law of large numbers).

Poor people don't riot if their poverty is perceptibly, contiguously improving over time. Rich people don't incite malign ideologies if there aren't poor people who will act as foot soldiers absorbing the brunt of adverse consequences of swearing fealty to such beliefs. When there is a chicken in every pot, people will riot over sports teams, but not politics. Actual getting-policies-and-legislation-established-and-practiced politics is dead-ass boring to the vast majority, so getting this many people to even pay attention to just the cartoonish depictions of politics we see in the US now is a major signal. I currently don't think it is a good signal. And I suspect it is a more complex signal than "get the wrongthink upper middle class suburbanites to shut up". But I'm just a layperson throwing some brush strokes out there and wanting to hear thoughts from folks like you. I hope I'm wrong-wrong-wrong since I'm operating from very limited data. I don't know what the hell the on-the-money forecasters are making of all this, but in a world this big, I gotta believe there is someone or some entity out there that has had access to sufficient data and has been consistently right for a couple decades plus, and some very wealthy people are paying very dearly for their ongoing analysis.