Amid escalating calls from within his own party to drop out of the 2024 presidential race following a catastrophic debate performance last month, President Joe Biden announced Sunday afternoon that he will not seek reelection and endorsed Vice President Kamala Harris for the Democratic nomination.

In a letter posted to his X account, Biden stated that while it has been his “greatest honor” to serve as president and that “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 followed up the announcement with another post shortly after offering his “full support and endorsement for Kamala to be the nominee of our party this year.”

The president, who will turn 82 in November and has faced increased speculation of suffering from Parkinson’s disease, did not specify a reason for dropping out of the race but noted in the letter that he would “speak to the Nation later this week in more detail about my decision.”

Over the last week, a steady drumbeat of Democratic lawmakers joined the ever-expanding list of those calling for Biden to drop out of the race. By Friday, the number of congressional Democrats calling for his exit surpassed 30, with Senate Majority Leader Chuck Schumer (D-N.Y.), former House Speaker Nancy Pelosi (D-Calif.), and House Minority Leader Hakeem Jeffries (D-N.Y.) all privately urging the president to drop out.

But over the last four weeks, Biden and his closest allies continued to publicly rebuke the burgeoning effort to convince him to step aside. After Biden contracted COVID and isolated himself at his Rehoboth Beach, Del. home four days ago, speculation continued to mount about whether he would stay in the race. However, just 19 hours before his drop out announcement, Biden posted, “It’s the most important election of our lifetimes. And I will win it.”

The president’s change of heart apparently came suddenly, reportedly “stunning” White House and campaign aides. It was such an “abrupt” decision, reported Politico, that “the campaign blasted out a fundraising email for ‘Joe and Kamala’ at 1:54 p.m. — eight minutes after Biden announced he was stepping aside.”

The swiftness of the decision has thrown the race for the Democratic nomination into a cloud of uncertainty. As has been reported, even though Biden has already won almost 3,800 delegates (more than enough to secure the nomination), and even though he has endorsed Harris, “the delegates who were pledged to him are under no obligation, according to the Democratic National Committee’s rules, to follow his lead and support his chosen successor.”

Controversy is also brewing about whether Harris is entitled to the almost $100 million that has already been raised by Biden’s campaign effort. Former Republican National Committee counsel Charlie Spies argued in a recent Wall Street Journal op-ed that campaign rules stipulate that Biden would be able to transfer his war chest to Harris only after he has been officially selected as the Democratic nominee.

Meanwhile, top Republicans such as House Speaker Mike Johnson (R-La.) are calling into question the validity of Biden’s decision in light of the nomination process. Shortly after Biden’s announcement on Sunday, Johnson posted, “At this unprecedented juncture in American history, we must be clear about what just happened. The Democrat Party forced the Democrat nominee off the ballot, just over 100 days before the election.”

He continued, “Having invalidated the votes of more than 14 million Americans who selected Joe Biden to be the Democrat nominee for president, the self-proclaimed ‘party of democracy’ has proven exactly the opposite.”

Johnson further reassured the country that “Regardless of the chaos in the current White House, our adversaries around the globe should be reminded that the U.S. Congress, the U.S. military, and the American people are fully prepared and committed to defend our interests both at home and abroad.”

Johnson concluded by calling for the president’s immediate resignation. “If Joe Biden is not fit to run for President, he is not fit to serve as President. He must resign the office immediately. November 5 cannot arrive soon enough.”