Heckuva of a lot to unpack here, but there's one piece of this that I don't think is being addressed.
The conversation thus far has been highly US focused, probably because the population of this board is majority US. But this is not a US only phenomenon, and I think the global spread of nationalist populism is worth consideration.
Numerous countries, particularly those in Europe but also in the Philippines, India, Brazil, Turkey, etc., have been electing and consolidating power in nationalist leaders who are either outright authoritarians or, at least, show some authoritarian tendencies. FWIW, I think Trump falls into the latter category. Modi belongs there too, I think, though I've not followed it that closely. Orban, Erdogan, Duterte, Xi, and Putin I would classify as outright authoritarians. Too soon to tell on Bolsonaro, though he has authoritarian tendencies for sure. Obrador in Mexico stands out as one of the sole left-leaning populists to rise to power, but has taken on a similar "strongman" ethic.
A few threads emerge from these leaders.
-disrespect for traditional democratic institutions, particularly surrounding the media and the rule of law. No accountability under traditional systems of checks and balances.
-blaming a shadowy "elite" for keeping prosperity from the larger population
-scapegoating an "other" who is set up as in opposition to a true citizen. The scapegoated group is often migrants (see Europe and the US especially), but homosexuals and religious minorities and “leftists” have also been targets.
-Most importantly, a cult of personality around the leader, drawing on tropes of traditional masculine power - strength, uncompromising policies, inflammatory rhetoric, willingness to use force--and holding up that leader as the only one who can deliver the country for the people
Each country’s history and culture gives their version of nationalism its own unique characteristics. But I think the broader implication is that the age of multilateral cooperation between nations may be coming to an end. If there’s anything that could be called a Trump Doctrine, it seems to be a focus on bilateral agreements and relationships where each side is trying to maximize benefits to their citizenry, regardless of how it effects the citizens of any other country. It’s highly transactional, and I sort of get the appeal of “I’m going to do what’s best for my people, and I’m going to assume you’ll do what’s best for yours, and we’ll see who wins at the end of the day.” But it doesn’t make room for long term negotiations where trust becomes an important factor. And it strikes me as a really bad way to solve complex global problems. And at this point, all our problems are complex and global!
As to what it’s highlighted? I think the clearest thing for me is that our education systems are failing a large number of people, and with the proliferation of information on the internet, many people (even highly educated ones) are struggling to differentiate useful facts from propaganda, half-truths, and manipulation. It used to be authoritarians had to suppress a free press. Now they just have to let actual facts drown in misinformation. Most people shrug, and because they don't know who to trust, they trust only those who appeal to their preconceived ideas.
TL / DR: It’s not just the US. It’s everywhere. And it’s not good.