When Americans cast their ballot for November’s election, they will be voting for the two oldest Presidential candidates in history: Donald Trump will be 74 on Inauguration Day, and Joe Biden will be 78. The age of these men, as well as the President’s recent hospitalization for COVID-19, raise the awkward question of what happens if they should die before or shortly after the election.

The U.S. Constitution provides clear rules in the case of the death or incapacity of the President and Vice President during his or her term. But the law is less clear when it comes to what happens when a presidential candidate dies near Election Day—a gap that could put U.S. democracy under further strain if such a tragedy should occur.

Here’s what the law says about what could happen in the unlikely event Trump or Biden should find themselves unable to assume the presidency.

If a candidate dies, can’t they put someone else’s name on the ballot?

No, at this point it’s too late. According to Jason Harrow of Equal Citizens, a nonprofit that seeks to improve U.S. democracy, many voters have already cast their ballots. He notes that U.S. law requires military voters to receive ballots at least 45 days before the election—so redoing ballots is out of the question.

Does this mean voters could be stuck with a deceased candidate?

Technically, no. That’s because the electoral college system means voters don’t vote directly for President but for the candidate’s respective electors—a group of party officials who choose the President on behalf of their state’s voters.

So can the electors simply choose someone else if the candidate dies?

This is where it gets messy. The Supreme Court recently upheld laws in various states that punish so-called faithless electors, who cast their vote for someone else. The decision involved Colorado electors for Hillary Clinton who voted instead for former Secretary of State Colin Powell in 2016. The court made clear electors do not have discretion to pick someone else.

A footnote to the Supreme Court’s ruling, however, suggested states could release electors from their obligation in the event the candidate died. For practical purposes, Harrow says, the political parties—in the form of the DNC or RNC—would tell the electors whom they should vote for instead. This would almost certainly be the vice presidential candidate, Kamala Harris or Mike Pence.

What if the candidate dies right after the election?

This would also be a messy situation. While Election Day is Nov. 3, the electors only meet in their respective state capitols to choose the President on Dec. 14. If Biden or Trump should die during this interval, the political parties would likely provide guidance for the electors to choose the vice presidential candidate instead.

There is also another key interval: the time between when the electors choose the President-elect, on Dec. 14, and Inauguration Day, which falls on Jan. 20. If the winning candidate dies during this time, the situation is less complicated. According to Harrow, the rules on presidential succession—set out in the 25th Amendment of the Constitution and a 1947 succession law—would be in effect. In this case, he says, the Vice President–elect would assume the presidency on Inauguration Day.