What happens if a US presidential candidate dies?

Joe Biden and Donald Trump are the two oldest candidates in US history. If either needs to be replaced, what next?

Americans are bracing for a rare presidential rematch between the two oldest candidates in US history: the 81-year-old president Joe Biden and the 77-year-old former president Donald Trump.

Concerns about their age, mental fitness and the possibility that Trump could be convicted of a felony and sentenced to jail time have raised questions about what would happen in the extraordinary event one of them dies, becomes incapacitated or abruptly withdraws.