Dexamethasone can have pretty strong psychoactive side effects. If he wasn't such a piece of garbage, I'd excuse him for being "high". But he doesn't give a toss about other people and thinks very highly of himself all the time.
Be interesting to see his general demeanour when they wean him off - he'll go from stupid stoned Trump to stupid grumpy Trump, should be fairly obvious.
The "haven't felt better for 20 years" comment from him was probably true. He's fat, has an awful diet, and the only exercise he seems to get is driving a golf cart. He's visibly shuffling - has the "old man walk" and is stooped. "Normal" for him at 74 probably isn't great. Dexamethasone will fix that dramatically, for a while, then... problems.