Louis Jacobson at PolitiFact:
What happens to a candidate if they die sometime before Election Day?
The timing of a death matters.
If the death happens prior to Election Day, then whichever is the relevant party organization — the Republican National Committee or the Democratic National Committee — would consult with its members and choose a new nominee, under slightly different rules established by each party.
If the death occurred earlier than October, sometime shortly after the conventions, the parties would have needed to update their ballot lines in every state. But with ballot deadlines now passed, ballots printed, and early voting underway in many places, that’s not feasible.
"What’s most likely is that the election would take place on time, with the deceased or incapacitated candidate’s name on the ballot, and then there would be a question if legislatures would allow presidential electors of each state to vote for someone other than the deceased candidate," wrote Richard L. Hasen, a professor of law and political science at the University of California-Irvine.
What happens if a candidate dies after the votes have been certified but the electoral college hasn’t cast its votes yet?
If this were to happen, "the electors may coordinate upon a substitute name, presumably one agreed upon by the national party committee," said Gregory Koger, a University of Miami political scientist. A natural choice for the parties would be the vice presidential candidate on the ticket. Alternatively, the party could urge electors to continue voting for the deceased candidate.
Electors in recent history have been chosen by each party based on strong party loyalty, and some states punish electors for choosing someone other than their party’s nominee. So most would probably follow the party’s guidance. Still, they could have some degree of free agency, and if the election is close, only a few mavericks could cause difficulties.
"Electors are both plausibly free agents and plausibly bound by state law," tweeted Matt Glassman, a senior fellow at Georgetown University’s Government Affairs Institute. "That is, they might feel free to vote for whoever they want, or they might be compelled by state law to still vote for the deceased candidate."
There could be other types of "mischief," Hasen wrote. For instance, legislatures could decide to forward a slate of electors to Congress that ran counter to the voters’ intent. That would be most likely in states where the legislature is of a different party than the winner of that state’s presidential election.
Richard H. Pildes, a constitutional law professor at New York University, floated one potentially messy scenario: The party choosing the replacement nominee could be deeply divided, and electors do not coalesce around a single replacement candidate. This could prevent a single candidate from winning a majority in the electoral college. In that scenario, the House of Representatives would have to choose from the top three Electoral College vote-getters, with each state getting one vote.
"In that case, one or two faithless electors deciding to support, say, Sen. Mitt Romney and allowing him to enter the top-three could potentially give us a candidate the people didn’t even see on the ballot," Pildes wrote.
Currently, the Republicans have a narrow edge in state delegations in the House, even though Democrats control a majority of seats in the chamber. But the election results this fall could end up giving Democrats an edge.
There is one historical precedent, though one that probably doesn’t carry much weight today. Presidential nominee Horace Greeley, who lost the 1872 election to President Ulysses S. Grant by a wide margin, died on Nov. 29, 1872. When his 66 electors cast their ballots, 63 of them voted for someone else, mostly not for his running mate. But Grant’s margin made the exercise purely academic.
