The order marked a significant escalation in Trump’s targeting of political adversaries and could lay the groundwork for arguments by the Republican that a range of Biden’s actions as president were invalid.

Biden responded in a statement Wednesday night: “Let me be clear: I made the decisions during my presidency. I made the decisions about the pardons, executive orders, legislation, and proclamations. Any suggestion that I didn’t is ridiculous and false.”

The Justice Department under Democratic and Republican administrations has recognized the use of an autopen to sign legislation and issue pardons for decades, Trump presented no evidence that Biden was unaware of the actions taken in his name, and the president’s absolute pardon power is enshrined in the U.S. Constitution.

“This conspiracy marks one of the most dangerous and concerning scandals in American history,” Trump wrote in a memo. “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.”

Trump directed Attorney General Pam Bondi and White House counsel David Warrington to handle the investigation.

It’s unclear how far Trump will push this effort, which would face certain legal challenges. But it reflects his fixation on Biden, who defeated him in 2020, an election that Trump never conceded and continues to falsely claim was rigged against him.

Trump frequently suggests that Biden was wrong to use an autopen, a mechanical device that replicates a person’s authentic signature. Although they’ve been used in the White House for decades, Trump claims that Biden’s aides were usurping presidential authority.

Biden issued pardons for his two brothers and his sister shortly before leaving office, hoping to shield them from potential prosecution under Trump, who had promised retribution during last year’s campaign. Other pardon recipients included members of a congressional committee that investigated the Jan. 6, 2021, riot at the U.S. Capitol.

Trump often suggests that his political opponents should be investigated, and he has directed the Justice Department to look into people who have angered him over the years. They include Chris Krebs, a former cybersecurity official who disputed Trump’s claims of a stolen election in 2020, and Miles Taylor, a former Department of Homeland Security official who wrote an anonymous op-ed sharply critical of the president in 2018.

Meanwhile, House Oversight Chairman James Comer of Kentucky, a Republican, requested transcribed interviews with five Biden aides, alleging they had participated in a “cover-up” that amounted to “one of the greatest scandals in our nation’s history.”

“These five former senior advisors were eyewitnesses to President Biden’s condition and operations within the Biden White House,” Comer said in a statement. “They must appear before the House Oversight Committee and provide truthful answers about President Biden’s cognitive state and who was calling the shots.”

Interviews were requested with White House senior advisers Mike Donilon and Anita Dunn, former White House chief of staff Ron Klain, former deputy chief of staff Bruce Reed and Steve Ricchetti, a former counselor to the president.

Comer reiterated his call for Biden’s physician, Kevin O’Connor, and former senior White House aides Annie Tomasini, Anthony Bernal, Ashley Williams and Neera Tanden to appear before the committee. He warned subpoenas would be issued this week if they refuse to schedule voluntary interviews.

“I think that people will start coming in the next two weeks,” Comer told reporters. He added that the committee would release a report with its findings, “and we’ll release the transcribed interviews, so it’ll be very transparent.”

Democrats have dismissed the effort as a distraction.

“Chairman Comer had his big shot in the last Congress to impeach Joe Biden and it was, of course, a spectacular flop,” said Rep. Jamie Raskin, the Maryland Democrat who served as the ranking member on the oversight committee in the previous Congress. “And now he’s just living off of a spent dream. It’s over. And he should give up the whole thing.”

Republicans on the committee are eager to pursue the investigation.

“The American people didn’t elect a bureaucracy to run the country,” said Rep. Brandon Gill, a freshman Republican from Texas. “I think that the American people deserve to know the truth and they want to know the truth of what happened.”

The Republican inquiry so far has focused on the final executive actions of Biden’s administration, which included the issuing of new federal rules and presidential pardons that they claim may be invalid.

Comer cited the book “Original Sin” by CNN’s Jake Tapper and Axios’ Alex Thompson, which details concerns and debates inside the White House and Democratic Party over Biden’s mental state and age.

In the book, Tapper and Thompson wrote, “Five people were running the country, and Joe Biden was at best a senior member of the board.”

Biden and members of his family have vigorously denied the book’s claims.

“This book is political fairy smut for the permanent, professional chattering class,” said Naomi Biden, the former president’s granddaughter.

Biden withdrew from the presidential race last summer after a debate against Trump in which he appeared to lose his train of thought multiple times, muttered inaudible answers and misnamed different government programs.

The disastrous debate performance pushed questions about his age and mental acuity to the forefront, ultimately leading Biden to withdraw from the presidential race. He was replaced on the ticket by Kamala Harris, who lost the election to Trump.