Republicans call on Biden to resign after he steps away from re-election bid

President Joe Biden's resignation just a month before the Democratic convention is an unprecedented moment in US politics

US President Joe Biden at Dover Air Force Base, in Delaware. He has been criticised by political rivals. AP

US President Joe Biden faces further political battles after his historic announcement that he will not seek re-election on November 5, with leading Republicans calling for him to resign outright.

Republican Speaker of the House Mike Johnson said on Sunday that "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," Mr Johnson wrote on X.

Mr Biden withdrew from the race on Sunday, and later endorsed his Vice President Kamala Harris as the party's candidate, although her nomination is not certain until after the Democratic Party convention next month.

Republican nominee Donald Trump responded with characteristically inflammatory language, claiming he "annihilated" Mr Biden in "an earth-shattering debate".

"He was not fit to serve from the very beginning, but the people around him lied to America about his complete and total mental, physical and cognitive demise," Mr Trump wrote on his TruthSocial platform. "Whoever the Left puts up now will just be more of the same."

Senator JD Vance, the Republican vice presidential candidate running alongside Mr Trump, said "not running for re-election 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".

"There is no middle ground," Mr Vance added.

Mr Biden's term in office is not the only target of Republican criticism around his decision to drop out of the 2024 campaign. The party is also challenging how the Democrats can replace him after Mr Biden swept the party's primary elections this year.

Congresswoman Elise Stefanik, a leading Republican on Capitol Hill, was among those critics, saying the Democrats are "disenfranchising the votes of 14 million voters ... all because they hid Joe Biden’s unfitness for office and now are reaping the deserved plummeting polls".

Mr Johnson, the highest-ranking congressman in the Republican-majority House of Representatives, earlier suggested that the Democrats could face legal challenges if Mr Biden were to step aside.

Speaking on ABC’s This Week before Mr Biden's announcement, Mr Johnson said: “Every state has its own system and in some of these, it’s not possible to simply just switch out a candidate.”

Congressional leaders are coming back to Capitol Hill on Monday after a short break, preparing for a busy legislative week and a controversial address by Israeli Prime Minister Benjamin Netanyahu.

The Republicans hold a slim majority in the House of Representatives, against a slim Democratic majority in the Senate. That means the Republicans would probably be unsuccessful if they tried to force Mr Biden out of the White House with an impeachment.

Democrats have, meanwhile, rallied behind Mr Biden's decision, describing it as an act of patriotism.

Democratic Senate majority leader Chuck Schumer said Mr Biden "put his country, his party and our future first".

Former president Bill Clinton and former secretary of state Hillary Clinton, who endorsed Ms Harris in a joint statement, said Mr Biden "restored our standing in the world".

"By any measure, he has advanced our founders' charge to build a more perfect union and his own stated goal of restoring the soul of our nation," they added.

Congressman Gregory Meeks, the leading Democrat on the House foreign affairs committee, led the influential Congressional Black Caucus in a quick endorsement of Ms Harris, who was the first black, South Asian and female vice president in US history, and would become the first female president if she wins in November.

Democratic House minority leader Hakeem Jeffries praised Mr Biden as "one of the most accomplished and consequential leaders in American history".

Mr Jeffries notably did not mention Ms Harris as the Democratic presidential candidate in his statement after Mr Biden's resignation.

Members of the progressive wing of the party, sitting to the President's political left, also thanked Mr Biden.

Senator Bernie Sanders, a progressive independent who caucuses with Democrats, said: "As the first president to ever walk on a picket line with striking workers, he has been the most pro-working class president in modern American history."

Progressive senator Elizabeth Warren backed Ms Harris's candidacy. "We have many talented people in our party, but Vice President Harris is the person who was chosen by the voters to succeed Joe Biden if needed," Ms Warren wrote on X.

"She can unite our party, take on Donald Trump and win in November."

The divisions around Mr Biden's decision were on display outside the White House on Sunday.

One visitor, Michale Wille, held a sign that read "Bye Joe". The Uber driver, 37, was angry at the President and the Democratic Party.

“The Democrats and the media conspired for years to tell us that Joe’s health was fine,” Mr Wille told The National. “We’ve all seen it.”

The back of his sign called on Mr Biden to resign from the presidency.

“If you can’t run for president, you shouldn’t be president,” he said.

Standing next to Mr Wille, Angles Dean held a small sign in red lipstick that said: “Thank you, Joe.”

The life-long Democrat said she wanted to show her support for Mr Biden and the party. “I was like, I don’t want Joe Biden to think that we’ve forgotten about him," she told The National.

"I have love in my heart for his struggle. I feel like he’s saved our country. I feel like he’s still trying to save our country."

Ms Dean said Mr Biden was putting the country before his own ego and that she would support Ms Harris if she were at the top of the ticket.

Willy Lowry contributed to this report in Washington