To me, it looked like the problem was not his brain, it was between his brain and his mouth. His brain knew what it wanted to say, his mouth took the long road to get there. And when you only have a minute or two to make your point, every second counts.
I am not saying that to try and gloss over the problem. But I’ve watched older relatives succumb to Alzheimer’s and dementia over the years, and this is not it. It’s different. It’s still bad for any older person, though, much less a President.