Deadlines? Rules? I give you... Democrats.
"Let Joe be Joe..."
Replacing Biden: Aug 19th to August 21 is the dem convention, there are 771 Super delegates , party regulars, and while that number is not enough to secure the nomination , they can get others to switch by staying together as a block. After the convention it is extremely unlikely and would probably not be on all 50 states so watch August and watch Newsome if he continues to ramp up his efforts .