It's funny how the right has been taken in by this. Basically, their propagandists go through literally thousands of hours of footage of Biden, looking for any moments where he loses his train of thought (or even moments that can look that way if cut just right), and they collect all those into "supercuts" to feed the morons. And it works brilliantly.
The only problem with the approach is that it only works for those who are confined to a pinhole-view of the real world -- seeing only those Biden moments their handlers want them to see. Since most right-wingers have effectively sequestered themselves in the right-wing-media echo chamber, that works for a time. But what do you do when they wander outside of that echo chamber, even briefly, and see a non-cherry-picked Biden performance in real time?
That was the problem the propagandists couldn't overcome in 2020. Sure, they'd managed to convince the dumbest people in the country that Biden was in the grips of dementia and was "locked in a basement" so he wouldn't embarrass himself. But then came the debates. Biden went on stage, with obvious mental clarity, strong recall, and excellent focus, and he utterly demolished Trump. Twice. All the post-debate polls agreed, and even the wingnut viewers could see it for themselves, though they'd never admit it. It completely demolished months of hard work by the propagandists to construct an alternate-reality caricature of Biden.
I'm sure that's the problem they're grappling with right now. Sure, they can again convince the imbeciles that Biden is suffering cognitive decline. That's the easy party. Hand them the right Youtube supercuts and they can be convinced of absolutely anything. But what do you do the next time the morons are let out of the echo chamber and they see the guy in real time? What happens the next time there are debates, for instance, and he again puts in a sharp and effective performance that embarrassed whatever clown the Republicans throw into the ring with him? They might end up having to dodge the debates entirely to avoid that.