Election Day 2024 is expected to be dominated by a rare presidential rematch between 81-year-old President Joe Biden, the oldest candidate in American history, and 78-year-old former President Donald Trump.
Even before the July 13 assassination attempt on Trump, there had been debate about the fitness of both men to serve given their age, cognitive ability and possible prison time, raising questions about what would happen if either candidate needed to be replaced, either by necessity or of their own choice.
This highlights the fragility of American democracy, said Saladin Anbar, a political science professor and senior fellow at the Eagleton Center for American Governors.
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“We've reached the point where one outlandish scenario could create a whole set of problems,” Amber said. “Not because we want to be depressed, but because there's so much at stake, we should be talking about these issues.”
If something were to happen to Biden or Trump, who would run for president?
While Biden is certainly the presumptive nominee, he has not yet been formally nominated as the Democratic Party's candidate for the 2024 presidential election. The Democratic Convention is scheduled to take place in Chicago in August, but there have been recent reports that party officials are seeking to speed up or slow down the nomination process depending on their support for Biden.
Republican delegates, meanwhile, have already formally nominated Trump as their presidential candidate, which they did so at the Republican National Convention in Milwaukee, Wisconsin, on July 15.
Nov. 5 will be Trump's third consecutive presidential run, putting him in line with just three other major party presidential candidates, including Henry Clay and William Jennings Bryan, to run by Election Day.
He almost didn't.
Just two days before securing the nomination, Trump joined the ranks of more than a dozen presidents and presidential candidates who have been targeted by gunmen. The first was former President Andrew Jackson, who survived unscathed on Jan. 30, 1835.
If Biden resigns, dies or is otherwise incapacitated, Vice President Kamala Harris would assume the presidency under the 25th Amendment to the U.S. Constitution. But the rules for nominees and presumptive nominees are more complicated and must follow election law and party practice.
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With Trump already nominated, the succession scenario is a little clearer: The Republican National Committee has two basic options: select a candidate according to party rules or hold another national convention.
Amber said Trump's running mate, J.D. Vance, would be the likely candidate. But he's not an automatic choice, and there could be a flurry of candidates trying to unseat Trump and Vance. Potential candidates include Tim Scott, Vivek Ramaswamy and Nikki Haley. Either way, Amber said a convention is highly unlikely.
In Biden's case, the Democratic delegates who were elected and loyal to him in the primaries, conventions and caucuses where he dominated would still be tasked with formally nominating a candidate at the national convention if he were unable to run. That would depend on the politics of the time, the mood of party leaders and perhaps what Biden himself says, Amber said.
“21st century politics is candidate-driven. When you don't have candidates, you fall back on the old ways of American politics, which are party-driven, boss-driven,” he said. “It all comes down to who's leading the party.”
It would be a similar process to the one Republicans would have faced if Trump were assassinated.
A replacement candidate would likely be chosen through a contentious process that involves public speeches, conference negotiations and closed-door meetings that many see as undemocratic in a modern system that relies on caucuses and primaries to circumvent party leaders, Amber said.
For Democrats, the process is also complicated by the existence of “superdelegates” — uncommitted delegates who people like Harris, California Gov. Gavin Newsom and Michigan Gov. Gretchen Whitmer lobby for support and who could swing the outcome of a contentious convention.
“It would literally be an indiscriminate attack,” Amber said.
What would happen if President Biden withdraws from the election?
In 1968, Senator Robert F. Kennedy was assassinated while competing with Vice President Hubert Humphrey and Senator Eugene McCarthy for the Democratic nomination after Lyndon B. Johnson withdrew in March of that year.
Kennedy was shot three times on June 5, just hours after winning the California primary, leaving a total of 393 delegates undecided. Senator George McGovern announced his candidacy to replace Kennedy and replace the delegates two weeks before the convention, but the delegates were divided between the candidates. The largest supporters supported Humphrey, who won the nomination despite not running in any state primaries.
In 1972, Senator Thomas Eagleton was the Democratic Party's vice presidential nominee, but withdrew from the race after the party convention. Responding to reports that he was receiving treatment for mental illness, Eagleton was replaced by former U.S. Ambassador to France Sargent Shriver during a special meeting of the Democratic National Committee.
A similar scenario would be possible if Biden were to withdraw from the race after winning the nomination at the Democratic National Convention. By party practice, the national committee is to consult with Democratic leaders, including members of Congress and state governors, before reaching an agreement on a replacement or an entirely new candidate.
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For both Biden and Trump, changing the name on voters' ballots may not be possible depending on the timing of events. To ensure all voters are informed, Anbar said, a move to change the ballots to reflect the candidates would be inevitable. But regardless of the name on the ballot, presidential voters vote for party electors in the Electoral College, and the ballots indicate party politics. Congress can postpone the election with the approval of the president.
But Anbar said the move would likely be challenged in court. Plus, the president's term is set to end: The 20th Amendment to the U.S. Constitution says the president and vice president leave office at noon on January 20. Congress normally convenes on January 6 to count the electoral votes and certify the election results.
In 1872, the Democratic presidential candidate Horace Greeley died after the election, but Greeley had already lost to Ulysses S. Grant and the electoral votes had not yet been cast. The party's electors were free to vote for another candidate or for Greeley. Congress decided not to count Greeley's vote. It is unclear what would have happened if Greeley had won. The electors might have acted to vote for their preferred successor, or they might have banded together for a successor nominated by party leaders.
