On Sunday, President Joe Biden has announced he is dropping out of the 2024 presidential race and endorsing Vice President Kamala Harris as his replacement.

Following a lackluster debate performance that kicked off a growing number of calls from fellow Democrats to withdraw, and testing positive for COVID-19 that resulted in President Joe Biden canceling upcoming rally the 81-year-old commander in chief has now announced his exit in a letter posted to his social media.

President Joe Biden had this to say, 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,” Biden wrote in a letter posted on X. “I will speak to the Nation later this week in more detail about my decision."

Biden’s decision to exit the race less than a month before his party’s convention and a few months before voters head to the polls is unprecedented in the modern political era.

The last sitting president to abandon a re-election bid was Lyndon Johnson, whose expansion of the Vietnam War in the 1960s split the Democratic Party. But Johnson’s announcement came in March 1968 eight months before that election.

Replacing Biden atop the Democratic ticket is likely to set off internal Democratic tremors as ambitious officials maneuver to become his successor. Factions have already formed around Harris, Whitmer and Newsom.

Harris, who at 59 is 22 years younger than Biden, would seem to be the heir apparent, but her approval rating stood at only 32% in an NBC News poll released earlier this month.

Unlike Republican delegates, who are bound to their candidate, Democratic delegates aren’t, so they are free to do what they want at the convention. Biden could have some influence over the delegates, but they could vote for a different candidate than his chosen pick, pending any rule changes at the convention meant to address this unprecedented situation.

The rules currently say that the delegates simply have to “in all good conscience reflect the sentiments of those who elected them.”