Honestly it's a little how my mom talks when she gets upset. Just a stream of things that are loosely connected but are all bobbing along on the same river of emotion.
It's how I get stuff like "You never call me you call your cousin he's cheating on his wife you know just because you broke up with your girlfriend doesn't mean you have to take it out on me". You can kind of see how there's a shared feeling or theme there but it's not articulated.
I'm going to guess that for someone who produces output like that, input of that type goes in easily. They're just vibing on the emotions.
It's one thing all the parodies like SNL miss. Every mockery of him makes more sense than his babble, because you need things to make some sense to be funny for more than 90 seconds.
"Covfefe" gives you what, two seconds of a joke? When you work it into something, that something ends up more coherent than actual Trump.