The Deep State didn't give him any choice. The guy who attempted to assassinate Trump was also researching Biden. While he preferred to whack Trump, he clearly would have tried to whack anyone that the Deep State told him to. When this became apparent to Biden, he conveniently caught Covid, so he could hide in his basement for a week to sort things out. He had only one choice, and took it.
Kamala Harris, the Vice President, becomes the immediate obvious replacement for Biden. She has succeeded this far in politics not from her political skills, but from her pussy power. The Democrats have to fabricate a resume for her if she has any hope of beating Trump. RFK Jr. is ready to hop right in, but the Deep State doesn't like him. Joe Manchin may jump in. He was probably clearing his plate all along, to provide for this. Hillary Clinton says she's not interested. She has so much baggage, that she's lucky just to stay out of jail. People mention Michelle Obama, but she claims to be not interested.