He is responsible for intentionally hiding his true mental state from the public. Running such a close race with Trump should be a clear sign of how unpopular he is as a candidate. At this point, Democrats are dangerously close to losing this election replacing him or not. That is on him.
Well, such moments in politics show us that rats do not, in fact, jump the ship first.
Still two groups of very shady people pitting a senile man (also a pro-Soviet politician in his younger years and probably a crook, but let's forget this) against a mentally impaired man (who could get a few life sentences were he not that important) look disgusting.