For Democrats, it’s trickier. In case of a pre-convention illness, a presumptive nominee could still accept the nomination in writing (which used to be the norm) or by a phone call. If the medical situation is more dire, Democratic delegates are not legally bound by candidate pledges, so a convention could, in theory, choose a different nominee. That’s even more obviously the case if the presumptive nominee were to die before the convention.

In that (or in a post-convention scenario), partisans of Bernie Sanders might make the case for their champion as the runner-up in pledged delegates, but it’s more likely the party would turn to more of a unity candidate who is also a bit younger than Biden or Sanders. If a vacancy arises after the convention, Democrats would probably go back to the days before widespread primaries and choose a substitute nominee via some sort of party leader consensus, according to New York University professor Rick Pildes, a rare expert on this subject…