One of the most effective ways to combat this is not doing Republican's dirty work by giving an ounce of credibility what they have to say on Biden's mental state. This is how they imbed false narratives into the minds of common Americans so that people only catch on to the extent they were deceived once it's too late and admitting naivety is too much a cost on one's sense of self-pride. It's like watching the James Comey bullshit happen all over again as if no one could ever know any better.