Plenty of people make this point regularly, but journalists who talk Trump should take the opportunity to just ask him to explain any basic factual matters. Like, "what is a tree?" OK, not that, but "what is Medicaid?" The point is not to prove he is a big dummy, though he is a big dummy, the point is that if he has no idea what he is talking about then nothing related that he says should be treated as being anything but gibberish. If the man thinks up is down there isn't much point trying to parse his views of gravity.
Journalists most of all should be interested in this. If you're wasting hours of your day trying to make sense of this man, you should have a better understanding of when it just isn't worth bothering. If Trump thinks Medicaid is actually a tree - possible! - then there's no point spending more time on it.