Is he having trouble recalling names of everyday objects and familiar people? Is he repeating sentences? These are the signs I would look for.
(Pat Summit's death made me read up on dementia.)
Yes.
From "something" (that he cannot articulate) about Obama, to the name of the EPA, to how he supported the Iraq War, terrorist groups he's previously denounced, Samuel L. Jackson, Serge Kovaleski, and David Duke, he regularly forgets people and things exist.
Repeating things, problems finding words (particularly complex ones), impaired social judgement, and problems with organization and planning are also signs of dementia.
Sound like a presidential candidate near you? (Hey, what do you know,
TrumpMiller really
is like Reagan!)