 There are a couple of reasons here that he's doing this. One is the political and the other is the imagistic. The last image anyone has in their mind of Joe Biden is him like this. Staring slack jawed, glassy eyed into the abyss from that debate last Thursday night. That is the last image anyone has. So the Democrats were trying to find some excuse for putting Biden back on the public stage to speak in a way that people would hear him.