TRUMP’S staff have opened a probe into whether Joe Biden was competent enough to sign pardons in the last days of his presidency.

Aides will assess if the series of pardons for death row inmates and family members were valid, given Biden’s alleged use of autopen.

One of those pardoned was his son, Hunter, whose case Biden long insisted he would not interfere with.

Ed Martin, Trump’s pardon attorney, indicated the investigation will evaluate whether Biden “was competent” and if individuals “were exploiting him through the use of AutoPen or other methods”.

An autopen is a device used to automatically attach a signature to a document.

Trump and his allies have alleged that Biden’s use of the device nullified his actions or implied he was not fully conscious of his decisions.

The current president even suggested Biden knew “nothing about” many of the pardons – supposedly rendering them “void and vacant”.

It is not known whether Biden did actually use autopen on his final-days pardons.

An email from Martin detailing the investigation said it will look at preemptive pardons Biden issued to several family members, and clemency he granted to spare 37 death-row inmates.

The death-row inmates had their sentences downgraded to life imprisonment.

In one of his last acts as president, Biden pardoned five members of his family, saying he wanted to protect them from future politically-motivated charges.

These went to his three siblings – James, Frank and Valerie Biden – and two of their spouses, John Owens and Sara Biden.

His son Hunter was pardoned slightly earlier on December 1 – absolving him after pleading guilty to tax violations and being convicted of illegally owning a firearm.

Hunter had been facing up to 25 years in prison for the offences, although was expected to receive a much lighter punishment as it was his first offense.

Martin’s email did not specify which member of Biden’s family would have their pardons investigated.

Nor did it reveal who had ordered the probe.

The President’s power to wipe away federal convictions or alter sentences is built into the US constitution.

Trump himself has used the tool liberally, such as when he signed sweeping pardons for almost all of the 1,600 supporters charged over the January 6 Capitol riots.

And Martin even said last month he views the presidential pardon power as “plenary” – which means it is absolute.

He said: “If you use the autopen for pardon power, I don’t think that that’s necessarily a problem.”

Maga figures have heaped doubt on Biden’s competency towards the end of his term.

In March, Andrew Bailey, Missouri Attorney General, wrote to the Justice Department requesting “a full investigation into President Biden’s mental capacity in his final days in office”.

He claimed that “Biden’s mental decline is famous” and suggested “staffers and officers […] may have exploited Biden’s incapacity” to the point that his orders could be deemed “null and void”.

Biden’s cancer diagnosis has provided Trump’s brigade with even more ammunition to level these claims.

Biden’s office confirmed last month he had advanced-stage prostate cancer which has spread to his bones after a lump was discovered during an examination.