@DavidMHarlan Maybe, but awareness of one's mental acuity is often the first thing compromised by dementia, so it's hard to say.
I have a feeling he's getting a lot of very bad news nowadays about his legal and corresponding financial woes, so that could also explain the sadness.
Honestly, he never wanted to be president, he just wanted to run for president, so I suspect he's been miserable since 2017.
Oh, and Melania probably doesn't let him touch her, and he's now too feeble to cheat on her.