President Donald Trump has ordered an investigation into his predecessor’s actions, Joe Biden and his staff, during his administration in the latest attempt to stoke outlandish “conspiracy theories”.

Mr Trump, in a move to discredit Mr Biden, issued an executive order to examine whether some of his predecessor’s presidential actions were legally invalid because his aides had allegedly enacted those policies without his knowledge.

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

A central claim of the conspiracy theory, as described by Mr Trump himself, is that Mr Biden’s use of the “autopen system”, which reproduces a person’s signature to be affixed to official documents, can legally invalidate those documents.

The development came after Mr Trump shared a media post over the weekend, claiming Mr Biden had been “executed in 2020” and replaced by a robotic clone, according to a New York Times report.

But Mr Biden slammed his successor, describing his claims as “ridiculous and false”.

In a statement on Wednesday, the former U.S. president said Mr Trump was only aiming to distract Americans as his administration works to extend tax breaks for the wealthy.

The executive order was issued after a recent disclosure that Mr Biden, 82, had been diagnosed with advanced prostate cancer.

Mr Trump and his Republican allies have long questioned Mr Biden’s mental acuity and have attempted to overturn some of the presidential pardons and federal rules issued at the end of his term in office.