President Joe Biden dropped out of the 2024 presidential race Sunday, he said in a letter posted to social media, creating an unprecedented vacancy atop the Democratic ticket one month before he was scheduled to officially accept his party’s nomination.

He will remain in office through the end of his term.

Biden’s withdrawal came after a weeks-long pressure campaign from party insiders following a disastrous June 27 debate performance against GOP candidate former President Donald Trump.

The move throws an already-unusual presidential race into further chaos, and it was not immediately clear Sunday how Democrats would choose a replacement for Biden in November’s election, though Vice President Kamala Harris would have a strong claim to lead the ticket.

Biden did not endorse a replacement, but praised Harris as “an extraordinary partner” in the administration’s accomplishments.

Biden, 81, appeared frail and confused at several points throughout the debate, leading to worries among elected Democrats and the party’s voters that he was no longer up to the task of governing or contesting Trump’s bid to win back the White House.