I do not think this is a sign of his dementia or incompetence with a teleprompter.
Listening to ungodly amount of senate and house hearings over the last 4-5 years, many legislators, though particularly those in the senate, will oft use quote, end of quote when including quoted dialogue in their statements and questioning.
Part of this is formality and part is that they tend to drone on and on, so if speaking in a monotone style as Joe does, unless he is whispering or screaming, it makes absolutely clear where the quote ends. He is particularly bad at run on sentences and various paths of butterfly thought making it harder to follow where a quoted phrase begins or ends.
It is a style he is accustomed to using, though I admit I have not gone back, nor do I intend to, and see if this is a style he has essentially always deployed.
In the mean time, he is effing up real issues that batter and there is plenty real, meaningful criticism to allow anyone to drag their huevos across the botox prepared face.