My sister (she's a Hospice nurse) was mentioning how certain medications can temporarily boost mental acuity in those with dementia. It would be interesting to know if Biden is on any medications of that sort.
Also, she mentioned once that when she'd seen Biden talking at other times, she noticed that he sometimes closes his eyes while he talks. That's actually another sign of dementia as the person does it to block out visual interference so they can concentrate better.