Tired old man does things any human would do if they were tired, is he fit for office?
Unfortunately, the fact that Dem Congresscritters have spoken up publicly asking him to step down means that:
Private channels are exhausted
Things are royally fucked.
Regardless of whether or not he is fit for office, those who are most dependent on a Dem ticket victory no longer have confidence in his ability to deliver it. That alone would be fatal. We need to get Biden to step down.