I can’t say I watch a lot of trump speaking (because I heard enough of that guy long ago). However, the few clips I’ve seen on trumps rambling feel like he’s trying to gain resonance with his audience (and failing). You can see pieces of this that worked for him during the the 2016 run. He’d mention some side topic, pause and watch for audience reaction, and if they responded favorable, he’d double down with a followup remark on that same topic. It many times came off looked semi-planned that that was where he was going to take the speech anyway back then even if that wasn’t the case.
These days it looks like he’s fishing for an audience response, gets none, sometimes switches back to the original topic, doesn’t get a response, fishing again, no response, fishing again, no response, repeat. Its like he blew threw his good material, and is grabbing desperately for something his audience will cheer for. Chasing a dopamine hit of people cheering for what he is saying…and not getting it. I think this is also why he’ll occasionally bring up Obama or Hillary because those (in campaigns now long past) hit his crowd very well. Where now those old reference just confuse his audience because they’re not relevant to any political discussions today, but trump isn’t saying any of this for political effect, but just to hear a crowd cheer for him so that doesn’t figure into his immediate thought process.