[This is something of a follow-up to An Arkansas Tea Party group plans an anti-equality rally. Guess what happens next...]
It is difficult to put exact dates on this but if you were growing up in a small Southern town between approximately the late 60s and the early 80s, you would hear a mixture of progressive and reactionary messages. The reactionary ones were overwhelmingly local and based on word-of-mouth. Blatant racism or sexism or anti-Semitism or old-style redbaiting were the kind of thing you might hear from neighbors and acquaintances.
By comparison, the national media you consumed in that pre-satellite, pre-Internet age, strongly tended toward the progressive. Norman Lear was the king of television. Nixon was a punchline. Even the Saturday morning cartoons preached diversity and tolerance. If you look at contemporary opinion polls, you can see that this is one of the few periods where both journalists and entertainers got significantly ahead of the social curve. The myth of a liberal media today owes a lot to its relative reality forty years ago.
Today, if you go to the small Southern town I grew up in, you will still hear plenty of reactionary messages, perhaps more than you would have heard back then, but the source has changed. If you actually talk with one of the locals who is voicing some extreme reactionary sentiment, you will generally learn that this comes directly from some kind of national media, be it cable news or talk radio or a website or a tweet on a smart phone.
In local interactions, there appears to have been real progress. Unlike 50 years ago, everyone in my hometown now knows someone who is in an interracial relationship or someone who is openly gay and no one seems to consider it that big of a deal. You'll find less tolerance in these towns than you will in a big city, but considerably more than you would have found in that small town (and perhaps in many major metropolis ) forty years ago.
In short, there's a bizarre combination of progress and regression. I know the standard explanation at this point is to go for some big sweeping social or demographic factor like economic inequality or white backlash, but I don't see how those fit what I've been seeing. I'm certain these things play a part, but more in the sense of fertile ground than direct cause.
Obviously, this is an immensely complicated problem, but if you had to reduce it to one simple hypothesis, I would say it would have to be that the rise of the Trump voter was the intended consequence of a massive and not particularly secretive social engineering experiment on the part of the conservative movement, an experiment that involved right wing media, the co-opting and in some cases simply buying off of religious leaders, and blatant Astroturf among other things. The rise of Trump is the unintended consequence of that same experiment.