Reagan, like Trump, is just a symptom. An even bigger symptom was Bill Clinton. Their policies hurried this along but they are just riding certain trends in American society that unfolded since Vietnam/Great Society:
1. Foreign Wars. The Cold War and Reagan managed to unite the right and the centrist left in favor of what the left calls the "military-industrial" complex. When it ended, these jobs began to collapse (see the eroding of the aircraft industry in California). But Republicans and Democrats continued to push nation building abroad which tired the American people of foreign wars.
2. Elitism. In the 50s society was a lot more mobile (at least for whites) and it was common to see a person build an industry by their bootstraps or a man to marry a secretary from another class. It's fiction, but in "Mad Men", Peggy Olsen graduates from secretarial school....now her job requires a top 20 college degree. Women began to enter the work force, and women (not wanting to throw away their effort at work) typically want to marry either someone of the same or similar status. Elites began to marry other elites, the college rat race began as colleges became gatekeepers, a society which valued technocratic experts arose. It's more likely a white woman graduating from an Ivy League school will marry an African American male graduating from such school than a white man rural farmer in Kansas. The elites have a vested interest in protecting this meritocrisy for themselves (which is why so many of us are in the youth soccer pay to play/college rat race).
3. Globalism. The elites have more in common with other elites in Hong Kong, Paris, or Moscow than a farmer in Iowa. Their concerns (on immigration, trade, monetary policy, war) are globalist. The D alliance on immigration, for example, is the rich which wants the cheap labor, and D politicians which want the vote, and the newcomers that want to bring over more friends and family or secure those who are already here. Those concerns often cut against the concerts of people lower on the economic totem pole. As society becomes more automated as well, there will be less well paying jobs at the bottom end and the pie has begun to shrink everywhere in the new globalist economy.
4. The Great Society. On the lower end of the government spectrum, the social safety net (separate and apart from arguments as to its necessity and proper structure) caused the weakening of family structures and the work ethic. It makes more rational sense for a woman with kids on welfare to go it alone than to share that pie with a husband who might be a drag on the family and throw away the money.
5. Racism. I'm a 3x minority....I don't believe America is "systemically racist"....I ascribed to the belief that everyone, regardless of skin color, is a little bit racist. But I also think there's racism out there, and it's often times the easiest reason for people to see why their lives may be in the crapper (rather than all the more complicated economic and societal stuff). And the history of America from it's founding through the civil rights movement was overwhelmingly concerned with racism and race.
6. The Collapse of Institutions. Back in Reagan's time, religion was the corner stone of the Reagan coalition. Trump just gives religion lip service, and the Mormons are uncomfortable with this new aggressive stance taken by the Republican Party. The churches, particularly the main line institutions, have collapsed. On the left, it's been replaced with wokeism/post-modernism. Other institutions as well have collapsed and been discredited. The pandemic for example has trashed the reputation of our health experts and teachers among a large segment of the population. The police are in disrepute among certain elements of the left. The press has trashed itself, and the tech industry is going down the way with it. The things which held us together are no longer there.
7. The Internet. Smashed gatekeepers to information (something which causes rage among the elites), and anonymity has led to inflammatory ways of dealing with each other.
All this to say, Trump's the dam, not the river....he's a symptom....things are going to get worse short of inspired leadership. The D reactions haven't exactly filled me with confidence, and frankly I'm not sure Biden is up to it...it would require a Lincolnesque figure. Hope I'm wrong.