Calls for President Joe Biden to vacate the Oval Office after he announced he would not run for re-election this year are intensifying. amid further doubts over his 'fitness to remain in office'.

The octogenarian leader, who contracted Covid-19 on Wednesday, has resigned amid ongoing concerns about his physical and mental faculties, compounded by dismal approval ratings.

In a blunder that raised eyebrows, Biden erroneously introduced Ukrainian leader Volodymyr Zelensky as "President Putin" and then bizarrely called Donald Trump his "Vice President" during the NATO summit.

Piers Morgan, the inaugural victor of Trump's The Celebrity Apprentice and ex-CNN anchor, has provocatively suggested that Biden's withdrawal from the race isn't enough.

His tweet read: "If Biden's unfit to stay in the presidential race, then surely he's unfit to remain President too?"

Trump took to Truth Social to assert that Biden "wasn't capable of being president."

He declared: "Crooked Joe Biden was not fit to run for President, and is certainly not fit to serve - And never was! ".

Morgan also disclosed that he had a telephonic conversation with Trump earlier.

His account of the call: " Donald Trump called me last night after watching this segment and we had a 15-min chat about bullets, Biden, the presidential race, Jagger, bleeding ears, and the elixir of eternal youth."

"Never known him sound so chilled which is pretty astonishing given he was shot a week ago."

Biden has consistently denied allegations of being unfit for office and the need to pass on the mantle, but recently he seems to have become "receptive" to the idea of abandoning his re-election bid.

Following a medical examination in February, White House doctor Kevin O'Connor declared Biden healthy, describing him as a "healthy, active, robust male who remains fit to successfully execute the duties of the presidency".

However, doubts about Biden's mental capacity have been raised following a lacklustre performance in a TV debate with Trump.

In an interview recorded in Las Vegas on Tuesday, BET News host Ed Gordon asked Biden if there was anything that would make him reconsider staying in the race.

His response was: "If I had some medical condition that emerged, if somebody, if doctors came to me and said, you got this problem and that problem."