They can change out candidates at the convention, should Biden step down. Speculation has been Newsome but Michelle Obama is also another name floating around. There is just no way they can run Biden. The scandals and now this? It will leave the Democrats running on nothing but Trump hate. My thoughts on it anyway.
I'm not even thinking about scandals but rather his overall mental acuity. if it is at all questionable today what might it be like in 3 or four years?
Same holds true for Trump for that matter. The US constitution says nobody can be elected president who is under 35. Maybe it should also say nobody over 75.
FWIW Canadian senators face mandatory retirement at 75.