Combine this with the fact that 20% of Democrats last month polled said they believe Biden is demented (medically).
Via Rasmussen:
A New York Times columnist has urged likely Democratic nominee Joe Biden not to debate President Trump in the fall. Most voters think that’s a bad idea, although only just over half believe Biden is even up to debating Trump given ongoing questions about his mental health.
The latest Rasmussen Reports national telephone and online survey finds that 54% of Likely U.S. Voters think Biden is capable of debating the president. Thirty-six percent (36%) disagree and say he is not capable of such a debate. Another 11% are not sure. (To see survey question wording, click here.)