CNN — President Joe Biden says he is not seeking reelection in a letter posted to X on his official account. Biden says he will speak to the nation later this week in more detail.

“It has been the greatest honor of my life to serve as your President,” Biden wrote. “And 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’s departure capped off weeks of concern about the 81-year-old president’s stamina and mental capabilities and skepticism of his ability to effectively campaign against Trump and govern the country for another four years. Biden’s decision is also likely to raise questions about his ability to fulfill the duties of the presidency for the remainder of his term.

It’s the first time a US president has dropped out of a reelection run in decades, recalling memories of President Lyndon Johnson deciding against seeking a second full term in 1968 – though Biden’s decision comes months later in the campaign than Johnson’s announcement. It’s also the latest shocking development in a highly charged political campaign that has included an attempt on Trump’s life.

But not even the attempted assassination and its tumultuous effect on the race could pause the loss of support Biden was facing among congressional Democrats who became increasingly convinced that a wipeout in November would also drown their down-ballot contests as well.