I'm not American so take what I'm saying with a grain of salt. My mom has late stage Alzheimer's so sadly I'm able to spot the signs of dementia early on. I haven't seen a lot of footage of Biden speaking but the ones I've seen you can see some dementia. Not in his speech, but in his eyes. I don't know how to explain it. It's a type of starting I see in all of the people in the geriatric home my mom now lives. Dementia or Alzheimer's affects speech when it's too advanced because both conditions affect cognitive abilities first, *then* motor skills