I also don’t see a lot of evidence that he is mentally unfit (for his age) as far as I am aware.
Curious, have you even heard of his gaffes and other funny stuff (Corn Pop, pony soldier, trueananashabadapressure, falling, not knowing where to go after a speech)? There are so many funny moments from his speeches. People put together “best of” compilations on every video site. They don’t get reported on CNN and stuff, you do have to look for them.
The mental fitness stuff is exaggerated for the most part, but he does lose track of his line of thinking when speaking off the cuff, without a teleprompter. He will start reciting a story he’s told 1000x, then he just sighs and says, “anyways…”
I would say, as with Trump, to go to as original of a source as you can. Watch an hour long campaign really or whatever to hear the whole speech in context. Don’t just read a headline or synopsis from the media.