You'd see it in personal conversations

A number of Republicans have grudgingly acknowleged he's still annoyingly with it. You'd also see it more in Q and A.

Even early alzheimers people have some totally off the rails moments.

Age related slowing can get bad enough where you can't be POTUS but you can be pretty functional. I don't think Biden's there but he could be in 4 years. That's why I wish he'd have opened the primary up a year ago.

I just think from both a personal mental competence and advisor perspective he runs circles around Trump. I wish the Republicans would nominate Whaley or someone who'd beat him. I'd dislike their politics, but I'd prefer we set a higher floor for the country.

Alas that's not the world we live in.