Two things
Trump’s appearance: prednisone. I strongly suspect he takes prednisone. It has 2 side effects other that its main anti-inflammatory purpose. First, in many people it makes them very irritable and intemperate. Second, water weight. Particularly in the face. I always suspected that Bob Dole took it to mask his sunken cheeks. And when he hollowed out after his last run, I felt sure.
Time comes for everyone and Trump is now older than Biden was in 2020. I didn’t listen to the Musk interview, but apparently Trump is now either lisping or slurring his words. Prednisone doesn’t help language decline. Or vanity. I have seen pictures of Trump without his dusting of Cheeto dust, and underneath his makeup his now sunburned skin has cracks like an unplanted field in a drought. Maybe he felt that at least one candidate should run without makeup.
About his speech decline revealing the toll of age, what’s good for the goose, eh? If he continues the race but has to withdraw due to age, several states have strict laws about appearing on the ballot. Ironically , one of them is Ohio. At this point I don’t think the Republicans can substitute anyone.