A senior official in Republican U.S. President Donald Trump's Justice Department told staff on Monday that he has been directed to investigate clemency granted by Democrat Joe Biden in the waning days of his presidency to members of his family and death row inmates.

Ed Martin, the Justice Department's pardon attorney, wrote in an email seen by Reuters that the investigation involves whether Biden "was competent and whether others were taking advantage of him through use of AutoPen or other means."

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An autopen is a device used to automatically affix a signature to a document. Trump and his supporters have made a variety of unfounded claims that Biden's use of the device while president invalidated his actions or suggested that he was not fully aware of these actions. It is not known whether Biden used autopen on pardons.

The email stated that Martin's investigation is focused on preemptive pardons Biden issued to several members of his family and clemency that spared 37 federal inmates from the death penalty, converting their sentences to life in prison.

Just before he relinquished the presidency to Trump on January 20, Biden pardoned five members of his family, saying he wanted to protect them from future politically motivated investigations. The pardons went to Biden's siblings James Biden, Frank Biden and Valerie Biden Owens as well as their spouses, John Owens and Sara Biden. Biden on December 1 pardoned his son Hunter Biden, who had pleaded guilty to tax violations and was convicted on firearms-related charges.

Martin's email did not specify which pardons of Biden family members were being investigated. It also did not make clear who directed Martin to launch the investigation.

A Justice Department spokesperson did not immediately respond to a request for comment. A Biden spokesperson did not immediately provide comment.

The U.S. Constitution gives the president broad power to issue pardons to wipe away federal criminal convictions or commutations to modify sentences.

Trump himself has made extensive use of executive clemency. For instance, he granted clemency on January 20 to all of the nearly 1,600 of his supporters who faced criminal charges in connection with the January 6, 2021, attack on the U.S. Capitol, which was a failed attempt to prevent congressional certification of Biden's 2020 election victory over Trump.

Martin previously served as the interim U.S. attorney in Washington before his nomination for that post foundered in the Senate.

Martin told reporters last month that he viewed the presidential pardon power as "plenary," meaning it is absolute.

"If you use the autopen for pardon power, I don't think that that's necessarily a problem," Martin said during a May 13 press conference, adding that he still felt the Biden pardons warranted scrutiny.

The investigation appears designed to use the Justice Department to amplify questions about Biden's health and mental acuity, a conversation that has intensified in recent weeks following his cancer diagnosis and a new book revealing Democratic concerns last year about Biden's condition.

Biden, who is 82, last year dropped his reelection bid amid questions about his mental acuity after a disastrous presidential debate performance. Biden was the oldest person to serve as U.S. president, and Trump is the second oldest.

Biden's closest aides have dismissed those concerns, saying Biden was fully capable of making important decisions.

No evidence has emerged to suggest that Biden did not intend to issue the pardons. In addition, a Justice Department memo from 2005 found it was legitimate for a subordinate to use an autopen for the president's signature.