One thing that I noticed, at the time that the Democrats are divided the Republicans seem to have unified in a way I haven't seen in a long time. I don't like that it is behind Trump, and wish republicans voted differently in the Primary...
I do think that swapping out the (selected not elected) presumptive nominee for the Dems will not be as positive for the Dems now as it would have been before it became obvious that the left and the press have been hiding signs of serious cognitive decline in Biden.
It isn't the age of the candidate, it is the extremely obvious (elephant in the room) cognitive decline.