I was alive and eligible to vote in 88 but I was a dumb kid that voted but didn’t pay attention to the primaries so I don’t remember him at all.
And he wasn’t a “great public speaker” in that he was known for saying dumb shit as you say. (If anything gaffe was a term that applied earlier to Dan Quayle, former VP).
I don’t recall for sure if the stutter was present then or to what degree.
I also don’t see a lot of evidence that he is mentally unfit (for his age) as far as I am aware.