It's not that he's lying, because he doesn't even know what the truth is. I also think he doesn't know that he doesn't know that. In this regard, I think of him as like a sophisticated bot: he doesn't track input in terms of true or false facts, but in terms of word-strings to say that are useful for his particular purposes. Any belief necessary to sound convincing is generated from the word strings.
My grandfather was a master salesman and as best I can tell, this was his basic approach to managing reality.
This happens on the other side of the fence, and no one bats an eye about it. In fact, they call it democracy, or something like that.
Snarkiness aside, if these people agree with him, then that is their vote. Really, we can't have democracy if we don't call it democracy when people vote the way we don't like them to. It's the same as free-speech: we can't suddenly abandon it if we don't like what's being said.
There's also a particularly ugly history of populists stirring up racial hatred as a means to power, which I think is especially dangerous.