Leaving aside the fact that Biden's dementia is completely irrelevant today, I'd argue that Trump is at a very similar stage.

Dementia manifests itself differently in each individual. With Trump, it's usually some sort of rambling, semi-coherent word salad, but he also had that confused appearance with Japanese PM Sanae Takaichi where he saluted at nothing, had to be led around from place to place in the room, and rather obviously had very little idea of where he was.

I'm honestly not pointing this out just because I oppose much of his politics or even because I find him personally distasteful. I was far from silent about Biden's decline, too. This is an issue with geriatric politicians regardless of faction.