Donald Trump has ordered an investigation into Joe Biden’s actions during his presidency, accusing aides of a “conspiracy” to “deceive the public about Biden’s mental state”.

In this latest move to discredit his predecessor, Trump took aim at the aides’ use of an autopen - a device that replicates signatures which presidents, including Trump, have used for decades - to sign executive actions.

“This conspiracy marks one of the most dangerous and concerning scandals in American history,” Trump said on Wednesday.

Biden slammed Trump’s move as “ridiculous”, saying his claims are aimed at distracting Americans as his administration works to extend tax breaks for the wealthy.