I believe that when the president speaks, itโs to the country, not to any specific group. The same should be said for any candidate running for the presidency, in this case Joe Biden.
If your theory is correct and Joe only speaks to his fellow dems, or coerces his supporters while ignoring the rest of America - is that a guy we want to preside over ALL US citizens?
What does that have to do with what large numbers of their voters believe?
If a candidate were to say, "I intend to have people with red hair shot on sight" then it's pretty freaking obvious that we can expect fewer people with red hair to vote for that candidate.
The candidate who says "I intend to have people with red hair shot on sight" doesn't have to "only speak to" people with blond, brown and black hair. That candidate can certainly say that to EVERYONE. But it is going to cause a probable shift in whether that candidate gets many votes from people with red hair.
It's pretty obvious that on the question of "Are you concerned about whether the risk of the viral pandemic might make it safer to vote by mail than in person?" you would get different percentages from Trump supporters and Biden supporters on whether they were concerned about the viral pandemic.
It has nothing to do with who they "speak to". Yes, Donald Trump told everyone that concern about the virus was overblown, and suggested it was a hoax. Surely you have heard him claiming that right after the election, everyone would open everything up and concern would vanish, since it was primarily being used as a political issue.
And sure he said those things "to the country, not to any specific group."
Likewise, Biden has said things
"to the country, not to any specific group" that the viral pandemic is real, and that the government needs to work constructively with epidemiologists on controlling the viral pandemic.
So, golly, people who believe the virus is a hoax are not going to worry about voting at polling stations, and people who believe the virus is real are going to exercise more caution and take advantage of mail-in voting.
That has nothing to do with whom either candidate "only speaks to". It has everything to do with the behavior of people who listen and believe one or the other candidate.
And that behavior is certainly going to be noticeable in which candidate's supports aren't worried about the virus and skew toward polling stations, and which candidate's supporters are worried and skew toward mail-in voting.
To interpret this blitheringly obvious point as some kind of assertion about who they are "speaking to" is hard to understand. The point is about who listens to whom and believes what.