Kamarck, Balz, Sabato
Their emails on the topic....
I’ve been told that the links do not work for everyone — although they do work for others. Such are algorithms. Here they are.
Kamarck
Here is an article I wrote on this topic that might be of help:
For deeper background you may want to have a look at my book on the topic of presidential nominations – now in its 4th edition. It gives a through look at the modern nominating season https://rowman.com/ISBN/9780815740506/Primary-Politics-Everything-You-Need-to-Know-about-How-America-Nominates-Its-Presidential-Candidates-2024-Presidential-Election-Edition
Candidates will be chosen as they have always been – by delegates to the 2 nominating conventions. The big difference is that these delegates may have much more independence of action than in previous years. The process however will be the same.
The primaries will, most likely, forecast the outcome but this year - between the age of the candidates and the chance that one could be on his way to jail – the selection of the actual delegates might be more important than results of the primaries
Yes, we could have a real convention – my book tells stories of how the pre 1972 conventions worked.
It will be the political parties. They are responsible for nominations and the Supreme court has upheld their primacy in that area for many years now.
No Biden does not have to endorse Harris
Right now no one in either party is likely to announce – filing deadlines are rapidly passing.
Nikki Haley is, right now, the best chance for the GOP to escape Trump’s grasp.
I am author of Primary Politics: Everything you need to know about how America nominates its presidential candidates.
Balz
The answer to your question is that the two national conventions would have the power to select their nominees and we could either have that long awaited brokered convention we've been talking about since you and I were working together, or some kind of deal would have been worked out ahead to avoid a nasty fight at the convention that would leave one or both parties even more divided.
Your other questions are good ones. Would Biden endorse Harris or would he say that there should be open debate and consideration of others who might want to raise their hands. The parties have shown then don't have that much influence – Trump's victory in 2016 is evidence of that – although the conventions are creatures of the parties. By Super Tuesday, most filing deadlines (maybe just about all) would have passed, so entering primaries might not be possible.
Money likely would not be much of an issue. Biden or Trump could transfer their campaign funds to someone else (I can't imagine Trump doing such a thing) but if other candidates wanted to run a pre-convention campaign, they could raise the funds and likely everyone of note would have a super PAC to help them (although super PACs, as Ron DeSantis has proven) are a mixed blessing.
Sabato
I’m on the road but the simple answer is that the national party committee (RNC or DNC) would really make the decisions. It depends on WHEN it happens after Super Tuesday. If soon after Super Tuesday, there are still lots of contests to go. The Republicans will consult their state parties and try to insure they are happy with arrangements, probably allowing for considerable variation among the states. Dems are more centralized with stricter rules, and the DNC could have a larger role—yet no doubt they will defer in large part to the White House since either Biden or Harris will be the sitting pIresident. Potentially, there could be challenges at the national convention, though I’d be surprised if any of them succeeded.
States with primaries cannot add names to the ballot once the filing deadline passes. It’s possible for parties to view the results as a beauty contest, and organize separate caucuses in some states. The likelihood is the delegates elected in a caucus, if sanctioned by the party, would be seated at the convention.