• Republican lawmakers are calling on President Joe Biden to resign after he announced that he will no longer seek reelection.
• "If Joe Biden is not fit to run for President, he is not fit to serve as President," Speaker of the House Mike Johnson said in a post on X. "He must resign the office immediately."
• White House physician Dr. Kevin O'Connor said in February that the president "is a healthy, active, robust 81-year-old male, who remains fit to successfully execute the duties of the Presidency."

Republican lawmakers are calling on President Joe Biden to resign after he announced Sunday that he will no longer seek reelection.

"If Joe Biden is not fit to run for President, he is not fit to serve as President," Speaker of the House Mike Johnson said in a post on X after Biden announced his decision. "He must resign the office immediately."

Other congressional Republicans, including House Republican Conference Chair Rep. Elise Stefanik and the National Republican Senatorial Committee, echoed Johnson's message.

"Biden is a national security threat in great cognitive decline and a clear and present danger to every man, woman, and child in our country," former President Donald Trump's campaign said in a statement.

"The question then to [Vice President] Kamala Harris is simple: knowing that Joe Biden withdrew from the campaign because of his rapidly deteriorating condition, does Harris believe the people of America are safe and secure with Joe Biden in the White House for six more months," Trump's campaign said.

Some Republican lawmakers have even raised the prospect of invoking the 25th Amendment, which dictates the order of succession if a president is no longer able to perform the duties of the office. Rep. Nancy Mace, R-S.C., said in a post on X that she planned to introduce a resolution on Monday urging Harris to invoke the 25th Amendment.

With just days left in Trump's term in office, the Democrat-controlled House of Representatives in 2021 passed a measure calling on then-Vice President Mike Pence and Trump's Cabinet to invoke the 25th Amendment. Pence refused to do so.

Biden, 81, has faced calls to drop out of the presidential race ever since his poor debate performance in June, where his verbal stumbles and hoarse voice elevated concerns about his age.

But the president did not cite those concerns nor his age in his announcement, and he made clear he will serve the 6-month remainder of his term in office.

"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 the letter posted to X.

After Biden's annual physical in February, White House physician Dr. Kevin O'Connor said that the president "is a healthy, active, robust 81-year-old male, who remains fit to successfully execute the duties of the Presidency."

Biden was also briefly seen by a doctor following the June 27 debate, he told Democratic governors the following week, and was told his health was fine.

The president is currently isolating in Delaware after testing positive for Covid-19 on Wednesday. O'Connor said on Sunday that Biden's symptoms have improved "significantly."

"The President continues to tolerate treatment without any difficulty and will continue PAXLOVID as planned," O'Connor wrote in the latest update. "He continues to perform all of his presidential duties."

Republicans' calls for Biden to resign began even before the president announced he would no longer seek reelection.

"If Joe Biden ends his reelection campaign, how can he justify remaining President?," Sen. JD Vance, Trump's running mate, said on X Sunday morning. "Not running for reelection would be a clear admission that President Trump was right all along about Biden not being mentally fit enough to serve as Commander-in-Chief."

But not all Republican members of Congress called on Biden to resign. Senate Minority Leader Mitch McConnell and House Majority Leader Steve Scalise in their statements both stopped short of saying Biden should not serve the remainder of his term.