I don't know what in the world is causing this trend in authoritarianism. But it's not just a US thing. I was just reading a Chris Hedges article about conservative right-wing Hindu majority trying to make Hinduism a national religion, and they are suppressing, and even have killed journalists who are reporting the truth about what's going on. And then there's Hungary, China and Russia. I think, unfortunately, Trump is shooting for membership in that club.
I think the irony is that people give up the need to trust in the truth when they are offered easy solutions to complex problems by people who promise them a magic wand. Think those immigrants are taking something from you? Just deport all their asses. Have you been promised hope for a return to better days? Who cares if those promises are laced with lies? The pull to buy in is seductive when it costs you nothing but your suspension of disbelief.