I wonder if his lawyers spoke to him about creating that impression.
I think he's legitimately in mental decline, too many crossed wires coming out as stories (All the "I talked to a dead person" stuff), and the arms while walking and the Roomba stuff.
That said, either him or his handlers (or both) hamming up the "Aw Shucks, I'm a forgetful old grandpa" shtick in any DOJ interviews is probably a sure bet. Also, let's be real, the DOJ would be looking for a plausible reason to decline to prosecute him, for sure. As much as he tries to come off as a genial old guy, I've seen enough lost temper, snapping ate reporters and voters to bet a decent bottle of whiskey that any prosecutor that tried could bait him in to a full Jack Nicholson "You Can't Handle the Truth!" speech on the stand. (with more 1940's colloquialisms)
I mostly responded to Ben, becasue like the rest of you, I've seen a ton of social media and YouTube versions of "Biden's DOJ even say's he's not fit!!11!!!", and when I read the actual report, I found that that is not at all what they said. In fact, since they said
they think he did it willfully, they just don't think they can convince a jury he did, the implication is they know he's playing it up, on purpose, but can't prove it.