Ahead of the November 5 presidential election in the United States, Republican candidate Donald Trump has issued a challenge to incumbent President Joe Biden, calling for both men to undergo a cognitive test to demonstrate their fitness for office.

“Joe should immediately take a Cognitive Test, and I will go with him, and take one also,” Mr Trump declared in a post on Truth Social on Friday. “For the first time we’ll be a team, and do it for the good of the Country.”

Mr Trump, 78, is three years younger than Mr Biden, 81. The duo are currently the leading contenders in the race for the White House.

Mr Trump’s challenge emerges amid mounting scrutiny over Mr Biden’s mental and cognitive faculties, spurred by recent debate performances and public gaffes. 

On Thursday, at the NATO summit, Mr Biden confused Mr Trump with his Vice President Kamala Harris and mistakenly identified Ukrainian President Volodymyr Zelensky as Russian President Vladimir Putin.

Before this latest incident, Mr Biden’s performance in a debate against Mr Trump had already sparked concerns about his cognitive health, with critics suggesting that age might be taking its toll on him.

Since the debate, Democrats have pressured Mr Biden to consider stepping down in favour of a viable candidate.

The New York Times, in an editorial, also suggested Mr Biden withdrawing from the race to make way for a stronger contender.

Despite the growing calls for him to resign, Mr Biden has remained resolute, stating that only God could persuade him to abandon his campaign.