There's one major principle in play here. I think it is one of times and seasons. Ideologies and their prevalence go round in circles. I think in the late 20th Century and early 2010s, liberalism gained a lot of ground. Then what follows is that people get fed up with the downsides of the ideology. All the PC garbage, loose borders amidst other points that liberalism sold are actually getting people sick. What we see with Trump and these other elections are just little signs of revolt that are bound to be experienced in most generations. Conservatism will also do its time, get people fed up and then the whole cycle continues