*(Yes I'm starting that far back.)
Having become smart and deadly, hominids become not only ecologically successful, but ecologically dominant. The only real selective threat was other hominids. This resulted in a troupe size arms race. However, this had an unexpected result: troupes became so big that most members would spend the bulk of their time interacting not with other troupes or the environment, but other ingroup members.
Thus hominids started to form three castes; the warriors, for dealing with outgroup conspecifics; the shamans or priests, for dealing with the nonverbal, nonstrategic environment; and the merchants, who dealt primarily with internal exchanges.
Surface area being what it is compared to volume, merchants are the most numerous caste. For them, the most important resource-acquisition skill did not involve contact with reality, but opposingly with fooling other ingroup members into thinking defection was cooperation, and of course of detecting and defeating the others' efforts to do same.
Result: the arms race stopped being group size, and become liar-liar competition. Humans now practice lying instinctively. Humans have exquisitely sophisticated lying assistance adaptations, such as the consciousness/subconsciousness compartmentalization. However, necessarily, this makes you smarter, and as a result of these two chained smartness arms races, human brain size has increased blisteringly fast over evolutionary history.
Perhaps the pelvic limits on brain size also helped shift the war from group size to liars. Brain spent on having a bigger troupe doesn't help as well for lying and detecting lies, and ditto neurons spent on killing instinct, so there's a tradeoff there.
Result: lying is natural. Agriculture thus inherently creates an environmental niche for a guild of liars. Expert craftsmen at exploiting lies for mind control. This guild will have its own subculture, techniques and tricks, and I call it Sophism, of which the earliest clear record is Protagoras. They are a perversion of the shaman caste: they use their grasp of reality, but are treating conspecifics like a natural problem to be manipulated, instead of as peers like the merchant caste do. Instead of shamans of the forest, they are shamans of the human.
For completeness I'll mention that super-Dunbar sized groups necessarily require anthropology; the science of being human; the shaman type very similar to Sophism.
Humans have strong egalitarian instincts from back before money evolved. With no way to store wealth and troupe size being critical to survival in war, every individual counted and hoarding was pure waste. Similarly, because a strongman is a defector, and defection harms the whole group, anyone who made themselves out to be too dominant was quite rationally torn down by a coalition.
Sophism, the apotheosis of natural lying instincts, can appeal to natural egalitarianism to propose an equal-sounding form of government: democracy. In theory everyone is in charge, but we still get the benefits of division of labour, by making someone else do the actual ruling.
Of course the wealthy know that it's two wolves and a sheep deciding what to have for dinner. Though in reality the wealthy are the wolves, thus two sheep and a wolf, and in reality the sheep are monkeys, so it's a wolf versus a monkey troupe. Before agriculture, troupe size mattered. After, army sized still mattered a whole lot even though armour disabled Lanchester's Square Law, and so the wealthy wolves tended to surrender to Sophist sophistry. Not to mention it soothes their own egalitarian guilt.
(And thus democracy is an envy/spite engine.)
Thus Sophists establish democracy, to establish a siphon between rich and poor, and skim some off the top. It's not like the irresponsible poor are going to notice there's some missing. Plus hey, free stuff.
When Rome fell, we entered a 'dark' age, where Sophism was lost. However, Islam kept (and subsquently suffered from, when Al Ghazali Sophisted them to death) enough texts for the Sophism virus to re-appear in Europe around 1100. Whereupon demogogues started reappearing, you got St. Francis, Luther etc. causing chaos, and ultimately...they lost their kings.
What is Progressivism? It is our particular strain of Sophism. Given a Hajnal folk who believe in Christianity, the easy lies are predictable. These lies get laid down as culture, and then new niches for lies appear on top of them, and thus Progressivism is largely predictable.
For now, I'll be brief about mentioning Sophism resistance, also known as Philosophy. Sophism is parasitism, so sooner or later the population adapts to resist the parasite. Lies are unstable form of predation, as they require the prey to trust the predator. No matter how well adapted, the predator cannot make the prey trust them.
Philosophy's root is the art of checking your facts. Generalized due diligence.
Democracy is socialist redistribution of power. Power is often used to acquire wealth. Democracy thus implies socialism of wealth.
Or more generally, democracy is in itself the defeat and surrender of wealth. The responsible are punished, and the irresponsible rewarded. The responsible etiolate, while the irresponsible multiply. As per Plato et al, the electorate degenerates, moving leftward, becoming ever more vulnerable to Sophist manipulation.
Full socialism is communism. Full communism is full equality. We are only equal in death.
As part of Sophism resistance, the responsible right starts noticing the irresponsible left voters are a problem, especially as responsibility declines so much that infrastructure starts to break down. For now, they're not realizing that responsibility is a spectrum. There's always a left half of the bell curve, who will suffer envy and independently be more vulnerable to Sophism. Even Massachusetts votes right 40% of the time. Only DC is pure, and that's probably due to filtering.
The Left is not the enemy. Even if the electorate was subject to drastic action and radically shifted right, there will still be a left half. The mind control parasites are the enemy.
More accurately, egalitarian hubris is the enemy. Envy is the enemy. Pride is the enemy. Lies and the lying instincts are the enemy. These ideas may be familiar...