His father died of Alzheimers which tends to run in families. It would not be surprising for Trump to develop it, if he hasn’t already, because his father had it.

Contributing factors to Alheimers are family history, poor diet and lack of exercise, all of which Trump has.

I think the biggest “tell” is if you go on YouTube and find recordings of interviews that he did decades ago. He is a complete different person. He speaks in whole, grammatically correct sentences, his vocabulary is much larger and he is able to stay on topic.

I live in NJ, adjacent to NYC, so I have had the opportunity to follow Trump and his career since the 70s. His dementia is very obvious.