Republican Party presidential candidate Donald Trump has questioned Joe Biden’s fitness to continue as president after he dropped his re-election bid.

Fox News quoted him on Sunday: “He is not fit to serve, and I ask — who is going to be running the country for the next five months?”

Echoing him, Mike Johnson, the Speaker of the House of Representatives said: “If Joe Biden is not fit to run for President, he is not fit to serve as President. He must resign the office immediately.”

Republicans overwhelmingly continued their attacks on Biden after he announced he was no longer seeking the Democratic Party’s presidential nomination.

The one notable exception was the Republican presidential candidate in 2012, Senator Mitt Romney, who said: “I respect President Biden. His decision to withdraw from the race was right and is in the best interest of the country.”

Writing with mangled syntax and capitalisation on Truth Social media platform, Trump said that Biden was “the Worst President, by far, in the History of our Nation. He has done everything possible to destroy our Country, from our southern border to energy dominance, national security, international standing, and so much more.”

Many Republicans lined up to repeat Trump’s attack in various forms.

Trump crowed: “He was annihilated in an Earth Shattering Debate, and now the Corrupt and Radical Democrats are throwing him overboard.”

After the June 27 debate in which his performance raised questions about cognitive abilities and his capacity to match Trump’s campaign vitality, Biden announced that he was dropping out of the race and endorsing Vice President Kamala Harris to be the Democratic Party’s candidate.

Trump alleged that “the people around him lied to America about his complete and total mental, physical, and cognitive demise” to prop up Biden.

“Whoever the Left puts up now will just be more of the same,” he said.

He told CBS on Sunday that Harris “could be far less competent [than Biden], which is hard to believe.”

CNN reported that he said that Harris will be easier to defeat than Biden.

On Saturday, at a campaign rally, Trump ridiculed Harris by mispronouncing her name.

He said: “Kamaala, I call her laughing Kamaala. Have you seen her laughing? She is crazy. You can tell a lot by a laugh. She is nuts. She is not as crazy as [former speaker] Nancy Pelosi.”

Trump’s son Donald Jr said: “Kamala Harris owns the entire leftwing policy record of Joe Biden. The only difference is that she is even more liberal and less competent than Joe, which is really saying something.”