Joe Biden‘s withdrawal from the 2024 presidential race and subsequent endorsement of Kamala Harris for the Democratic presidential nomination has sparked a number of questions — including whether he will choose to resign before his current term ends, which would create a vacancy in the administration.

According to the Constitution’s 25th Amendment, if the president of the United States resigns from office, “the Vice President shall become President,” at which point the new president “shall nominate a Vice President who shall take office upon confirmation by a majority vote of both Houses of Congress.”

In other words, if Biden opted to leave the White House early, Harris, 59, would become president and would then nominate someone to take her place as vice president. That person’s confirmation would require that both the Republican-controlled House and the Democratic-controlled Senate approve.

As for who, specifically, that person would be, it’s all speculative at this point. More than likely, Harris would choose the same person she’s eyeing for a 2024 running mate.

While the speaker of the House (currently Republican Rep. Mike Johnson) is next in the line of succession for the presidency, he would not be promoted to vice president. That line of succession only applies if both the president and vice president die or resign at the same time, in which case Johnson would become the commander-in-chief.

If Biden resigned, Harris would not be the first POTUS to nominate a new vice president mid-term — in fact, the vice presidency was vacated back to back in the 1970s.

On Oct. 12, 1973, Spiro Agnew resigned as vice president, leading President Richard Nixon to nominate House minority leader Gerald Ford as a successor.

The move came after Agnew was charged with bribery, conspiracy and tax fraud and urged to leave the administration. Agnew ultimately pleaded no contest to a single felony charge of tax evasion.

Ford would go on to become the 38th president of the United States in August 1974, less than one year after being sworn in as vice president, when the Watergate scandal caused Nixon to resign as well. Ford then nominated former New York Gov. Nelson Rockefeller to succeed him as VP.

On Sunday, July 21, 81-year-old Biden endorsed Harris to lead the party into November, putting her in a strong position with his delegates ahead of the Democratic National Convention. Biden’s endorsement came moments after he announced in a statement that he would be withdrawing from the 2024 race.

“While it has been my intention to seek reelection, I believe it is in the best interest of my party and the country for me to stand down and to focus solely on fulfilling my duties as President for the remainder of my term,” the statement read in part.

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As the oldest president in U.S. history, Biden has faced concerns about his ability to serve another term. His performance at the first 2024 presidential debate did little to quell those fears among Democrats, leading to heightened doubts about his cognitive health and calls for him to drop out of the race.

At 78 years old, Republican Donald Trump is now the oldest major party presidential nominee in U.S. history.