President Biden announced Sunday that he is dropping out of the race against former President Donald Trump, bowing to relentless pressure from Democrats who said his declining abilities and poll numbers would drag the party down and lead to a inevitable defeat in November.

The move upends the 2024 presidential race just weeks before early voting begins and leaves Democrats scrambling for a new ticket. Mr. Biden endorsed Vice President Kamala Harris to lead the ticket.

“It has been the greatest honor of my life to serve as your president,” Mr. Biden, 81, said in a letter published in X. “And while it has been my intention to seek re-election, I believe it is the best interest of my party and the country for me to step down and focus solely on fulfilling my duties as president for the remainder of my term.

“For now, allow me to express my deepest gratitude to all those who have worked so hard to see me re-elected. I want to thank Vice President Kamala Harris for being an extraordinary partner in all of this work. And allow me to express my sincere gratitude to the American people for the faith and trust you have placed in me.”