One of the early rules in life I learned (both work and personal) has been to never assume anything. It's dangerous.
While in the realm of fairness, I don't think the comparison with Reagan holds up. While Reagan was certainly showing signs of decline, he isn't as far gone as Biden with the stumbles, forgetfulness, dodging press conferences speeches and interviews, and getting lost mid sentence (which is a sign that he is really far advanced....my mother for example forgets she said things and loses things, but doesn't lose track midway through sentences...Biden didn't even do that last year during his limited public engagements).
I agree with the tear down thing. Since Obama, we've had Presidents who have only tried to tear down the other guy. But I also think the Rs have been tired of just taking things (like the Romney binders of women or the dog thing) and need to learn to fight back, particularly given how obvius the media has its thumb on the scale.
But I agree with watfly that the extent of Biden's dementia was not reported widely and the media went to great lengths to not report or focus on it. I don't think a single mainstream news outlet did a "Does Biden have dementia?" story during the election (only one I recall was CNN which tried to discredit the report as Republican propaganda). If he does have a capacity issue, it should have been fully explored and disclosed to the voters so they could make an informed decision. Unlike you, most of the left and media is still denying the dementia, and low information voters are only starting to get clued into it.