But if the president were to, hypothetically, withdraw from the race or find himself unable to run due to a health-related crisis, high-level Democrats could not simply find someone else to replace him at this point in the election cycle, as Haley or other observers have suggested, according to experts and party rules.

Depending on exactly when Biden were to withdraw from the race, in this scenario, his replacement would first be up to primary voters or, later, Democratic convention delegates or party members themselves. ...

If Biden were to die "in the middle of June when all the primaries are over, then it is only the delegates that get to decide," Kamarck said. But if Biden were to die "tomorrow, there would probably be some primaries that people would run in and get their own delegates elected. It's a timing question."