Nobody begins to tackle the constitutionality of Biden leaving after some of the primaries have closed. Every primary that has closed will not have had the opportunity to vote for whoever replaces Biden. The right will rip us a new one for installing a candidate without voting for them and for once they'd be right. With democracy on the line we cannot forgo democracy.
America doesn't have legal constructs around political parties so whatever the fuck the democrats do won't go against US law - its all just "tradition".
Democratic delegate voting rules require the delegates to "in good conscience" vote for who they were sent there to vote for unless they're released by that candidate. Realistically, an open convention will only happen if Biden releases his delegates.
Maybe? But they also might get sued and/or blacklisted from party politics. There was an interview with various delegates and even those who thought someone else should be the candidate they believed they were obligated to vote for Biden.
It's not entirely democratic at the convention, even in a typical election cycle. Recall that 15% of the delegates are "unpledged party leaders and elected officials" (superdelegates).
That aside, I don't think there's a constitutional issue here with respect to replacing Biden. If Dems decided to select the candidate via musical chairs or Parcheesi, to my knowledge that's a party matter (though voters would undoubtedly take a dim view of such antics).
It depends on how things are run, but unless there's a pre-decided consensus choice, multiple ballots would be likely.
And for this choice I'm not entirely sure it's wrong for party leaders and elected officials to have a vote. It's not like the Biden delegates were selected at random from the public to represent it in a momentous decision. No one thought the delegates would be anything other than a formality. They were likely selected as a reward for service to Biden or as a favor to some local official.
2018, right? But there hasn't been a contested convention since the rule change. Could be quite the circus, for good or ill. Multiple ballots more likely? Guess we'll see.
There hasn't been a brokered convention in the modern era of the primary system (post-1968). It would 100% be a circus. Good for TV, probably exciting, almost certainly bad for the party and its candidate. My guess would be that everything would be handled by the prospective nominees before the convention itself to avoid looking like a hot mess in front of the nation.
The West Wing had a brokered convention that went like seven ballots. Was a good episode IIRC.
There are no constitutional implications to a party's nomination process so long as it doesn't violate the law with regard to discrimination and the like. If Biden withdrew you get a brokered convention. If he withdrew after being nominated, the party's rules would place his VP nominee at the top of the ticket (although ballots would likely still have his name due to state laws and logistics).