Is joe bidens brain upto the job ?

He's probably not actually that dumb. It could be a farce so he doesn't have to answer questions or seem all that responsible. The idea of him being a sweet old man that eats ice cream makes him endearing to the public, even if he is dumb. The few times he's had to debate Trump he was on his A game. I don't think George W Bush was dumb either, he played up a goofy character and Dick Cheney portrayed himself as the evil guy that was in his ear.