"The propagandist's purpose is to make one set of people forget that certain other sets of people are human."
Aldous Huxley
Love Huxley, one of the true great of fantasy Sci-Fi
This is exactly what Trump supporters try to do to the rest of us and especially in social media. Why? It's because they have no facts and the ones they claim as facts do a backwards time travel until you forget the original subject matter.
I find that the best way to win an argument with them is to force them to stay on track of the original post, because they cannot then try to lead you in their discussion, and, they then have to try to concoct an argument within the matter at hand, and it inevitably ends up being so weak that it is easily destroyed. You are right though, 100%, their first tactic is to try to tangentialize the argument.