This is really shocking and worrying, the man is an ignoramus as well as an unstable racist misogynist who has no settled political views. It says a lot about the state of the US that such a man can be elected.
But this isn’t unique to the US. We’ve had Brexit in the UK. Berlusconi came and went but was something similar. And we have right wing populist parties with considerable support in France, the Netherlands, Germany, Poland, Hungary and beyond. The explanation in my view is that a lot of people have lost out as globalisation has ripped across the world and governments are so wedded to neoliberal ideas that little is done to protect the losers from the damage of change. In particular the Social Democrat parties that brought in the great post second world war settlement of full employment, the welfare state and reduced inequality have nothing to say. And if the left doesn’t stand up for those who are losing they swing to the populist right. We’ve seen it before in history and it is dangerous.