I'm not a Trump voter. But I would say It's rude and not generally true. I know a few coal miners, they seem intelligent to me. In fact, they are all more intelligent than I am when it comes to actually doing something practical! But I can clearly see that Trump is con artist, while most of them cannot, so there is a grain of truth in what you say. Where you go wrong is in being rude and not really understanding how these people think.
OK. The thing is, people that work with their hands ARE sometimes a little simple minded when it comes to politics. They see things simply. This is both good and bad. It's good because they can cut through a lot of the BS and get the main point out of something. It's bad, because they can become victims of a con artist like Trump. Unfortunately, too many of them have become victims of this narcissistic con artist.