The House Oversight Committee is intensifying its investigation into President Biden’s mental health fitness and his use of an “autopen” to sign official documents during his time in office.

The committee chairman, Representative James Comer, a Kentucky Republican, has sent letters to five former Biden officials asking them to participate in transcribed interviews. Among the targets: Mr. Biden’s White House physician, Kevin O’Connor; the former director of the White House Domestic Policy Council, Neera Tanden; a senior advisor to the first lady, Anthony Bernal; a former deputy chief of staff, Annie Tomasini; and a former deputy director of Oval Office operations, Ashley Williams.

“The cover-up of President Biden’s obvious mental decline is a historic scandal,” Mr. Comer said in a statement. “The American people deserve to know when this decline began, how far it progressed, and who was making critical decisions on his behalf.”

The committee chairman questioned the use of an autopen to sign executive orders and last-minute pardons before Mr. Biden left office. Hours before President Trump took the oath of office on January 20, the White House announced pardons for the former director of the National Institute of Allergy and Infectious Diseases, Anthony Fauci, and the retired chairman of the Joint Chiefs of Staff, General Mark Milley.

With fewer than 30 minutes left in his term, Mr. Biden also pardoned members of his family, including his brother James B. Biden and wife Sara, sister Valerie Biden Owens, brother-in-law John T. Owens, and brother Francis W. Biden. The former president pardoned his son, Hunter, for tax and gun crimes a month earlier.

“Key executive actions signed by autopen, such as sweeping pardons for the Biden Crime Family, must be examined considering President Biden’s diminished capacity. Today, we are calling on President Biden’s physician and former White House advisors to participate in transcribed interviews so we can begin to uncover the truth,” Mr. Comer said in the statement, adding that “obstruction will be met with swift and decisive action.”

The Department of Justice this week also announced that an investigation is under way following the release of audio recordings of Mr. Biden’s interview with Special Counsel Robert Hur.

The tapes, which were kept private by Mr. Biden’s attorney general, Merrick Garland, show that during an October 2023 interview with Mr. Hur’s team, Mr. Biden was barely lucid, suffering from repeated memory lapses as well as stumbling over his words. 

In his final report after a probe into claims that Mr. Biden mishandled classified documents, Mr. Hur decided not to press charges, saying “Mr. Biden would likely present himself to a jury, as he did during our interview of him, as a sympathetic, well-meaning, elderly man with a poor memory.”

In a Wednesday letter to Mr. Biden’s doctor, Mr. Comer said he wants “to investigate the circumstances surrounding your assessment in February 2024 that former President Biden was ‘a healthy, active, robust 81-year-old male, who remains fit to successfully execute the duties of the Presidency.'”

“The audio recording from Special Counsel Robert Hur’s interview with former President Biden is a startling reminder of the President’s rapidly deteriorating mental and physical condition,” Mr. Comer wrote to Dr. O’Connor.

In his letter to Ms. Tanden, who ran the Domestic Policy Council, Mr. Comer asked about reports of “Hunter Biden joining staff meetings and First Lady Jill Biden sitting at the head of the table of a Cabinet meeting.” He also raised concerns that Ms. Tanden was “involved in running interference on behalf of the former President and perhaps performing duties exclusively reserved for the President of the United States.”

On Tuesday, Mr. Trump said that Mr. Biden was not actually in charge of America when he held the White House, alleging that “radical left lunatics … were running our country.”

Speaking to reporters at the Capitol, Mr. Trump announced his intent to “look into” instances of autopen use following Mr. Biden’s recent disclosure of a prostate cancer diagnosis and the release of the Hur audiotapes. 

“Biden — look, it’s a very sad thing what happened, but we’re going to start looking into this whole thing with who signed this legislation. Who signed legislation opening our border? I don’t think he knew. I said, ‘There’s nobody that can want an open border. Nobody,’” Mr. Trump said. “And now I find out that it wasn’t him. He autopenned it.”

“Who was operating the autopen? This is a very serious thing,” he said. “We had a president that didn’t sign anything. He autopenned almost anything. He opened the borders of the United States of America.”