Since the day after election day, I and many other people have tried to figure out how all of this even happened. How did everyone left-of-center get it so wrong? The answer is provided in Adam Curtis' Hypernormalisation, released by the BBC in 2016. The documentary was released before election day, but Trump plays a prominent role nonetheless. I've attached a youtube link, because the BBC iPlayer only works in the UK. If you happen to live in the UK, I'd recommend watching it from their site as the quality of the youtube vid is simply not as good.
Once you've watched it, you'll wonder why you thought the election would end any other way...