Rick Hasen: “Assuming Biden voluntarily withdraws, there are two main election law questions: the rules of the convention, and the rules of ballot access. The rules of the convention are pretty simple in that delegates would be free to vote their consciences. (That would be true even if Biden stayed in the race.) Presumably, if Biden announced a withdrawal soon, a number of candidates would put their names in the ring. There might even be debates before the convention so that each of these people could be seen in prime time.”
“We are also early in terms of ballot access. Most state rules for major party candidates point to the convention winner as the presidential candidate. There could be some timing glitches in some places which could lead to litigation. There could be questions if Biden is on the ticket about presidential electors who under state law would have to vote for the candidate they were listed for. But I think we are early enough that most of the kinks would be worked out early.”
“So the bottom line is that there is unlikely to be an election law impediment to replacing Biden, should Biden choose to withdraw.”