US President Donald Trump on Wednesday ordered an investigation into what Republicans claim was a “conspiracy” to cover up Joe Biden’s declining cognitive health during his time in the White House.

The move, which was slammed by Biden, is the latest in a long-running campaign by Trump — with the backing of Republican Party politicians and their cheerleaders in the conservative media — to discredit his predecessor.

But it also comes as a growing chorus of Democrats begin to acknowledge the former president appeared to have been slipping in recent years.

Those concerns were thrown into stark relief by a disastrous debate performance against Trump during last year’s presidential campaign, in which the then-81-year-old stumbled over his words and repeatedly lost his train of thought.

“In recent months, it has become increasingly apparent that former president Biden’s aides abused the power of presidential signatures through the use of an autopen to conceal Biden’s cognitive decline,” a presidential memorandum issued on Wednesday reads.

“This conspiracy marks one of the most dangerous and concerning scandals in American history. The American public was purposefully shielded from discovering who wielded the executive power, all while Biden’s signature was deployed across thousands of documents to effect radical policy shifts.”

‘Ridiculous and false’

Biden vehemently denied the allegations.

“Let me be clear: I made the decisions during my presidency. I made the decisions about the pardons, executive orders, legislation, and proclamations,” he said in a statement shared with AFP.

“Any suggestion that I didn’t is ridiculous and false,” he said, slamming the ordered probe as “nothing more than a distraction by Donald Trump and Congressional Republicans who are working to push disastrous legislation”.

Republicans have long claimed that Biden was suffering from intellectual decline even as the White House pressed ahead with major legislation and presidential decrees during his term.

They cite his infrequent public appearances, as well as his apparent unwillingness to sit for interviews as evidence of what they say was a man incapable of doing the demanding job of Commander-in-Chief of the United States.

They insist that those around him covered up his physical and cognitive decline, taking decisions on his behalf and using a device that could reproduce his signature to allow them to continue to run the country in his name.

‘Autopen’

“The Counsel to the President, in consultation with the Attorney General and the head of any other relevant executive department or agency … shall investigate … whether certain individuals conspired to deceive the public about Biden’s mental state and unconstitutionally exercise the authorities and responsibilities of the President,” the memorandum says.

The probe will also look at “the circumstances surrounding Biden’s supposed execution of numerous executive actions during his final years in office [including] the policy documents for which the autopen was used [and] who directed that the President’s signature be affixed.”

Biden’s calamitous debate performance ultimately sank his bid for reelection, with key Democratic Party figures soon calling for him to drop out of the race.

But it was only several weeks later, after unsuccessful attempts to quieten his critics, that he withdrew, anointing his vice-president Kamala Harris, who eventually lost to Trump.

The Democratic Party is increasingly riven by squabbles about whether Biden could have been forced to step down earlier to give the party chance to find a more popular presidential candidate.

Biden’s former White House press secretary Karine Jean-Pierre on Wednesday criticised the in-fighting by the Democrats, calling it a “betrayal” of Biden and announcing her departure from the party as a result.

The fight has been given oxygen with the publication of a book by journalists Jake Tapper and Alex Thompson that claims the former president’s inner circle connived to keep him from public view because of his decline, which included forgetting familiar faces like Hollywood star and party stalwart George Clooney.

Trump’s claims of a cover-up were also boosted by news that Biden is suffering from an “aggressive” prostate cancer, with some voices on the right insisting — without evidence — the diagnosis must have been known some time ago to those close to the former president.