I was speaking in probabilities, not making a judgment myself (I wouldn't be qualified to do so anyway). Numerous mental health professionals have made the assertion that he is, and he has a family history of it, so at the very least it can't reasonably be claimed with 100% certainty that he's not in the early-to-mid stages of dementia.

Furthermore, my statement was very clearly presented as a massive stretch in the first place; noting that it might slightly increase the chance that he'll be unable to make an attempt at a third term (even if by 0.01%). Sometimes squinting hard enough that the resulting bokeh resemble a silver lining is all you can do to muster hope.

Statistically at his age he has a 25% chance of dieing before his term ends.