Hunter Biden’s new claim that his father’s disastrous 2024 debate performance was caused in part by his use of the sedative drug Ambien is becoming a new focus of the House Oversight Committee. Republicans on the committee are investigating reports of President Biden’s cognitive decline while in office, and whether the then-president’s family members and longtime advisers were governing in his stead.

Hunter Biden made his claim in an interview with an independent journalist, Andrew Callaghan, which was published Wednesday on YouTube. Mr. Biden said, somewhat confusingly, that his father was given Ambien prior to the debate because he was “tired as s—.”  

“I know exactly what happened in that debate. He flew around the world, basically, in the mileage that he could’ve flown around the world three times,” Mr. Biden, who received a pardon from his father late last year, told Mr. Callaghan. “He’s 81 years old, he’s tired as s—, they give him Ambien to be able to sleep, he gets up on the stage, and he looks like he’s a deer in the headlights.”

The trip to which the former first son referred concluded two weeks prior to the presidential debate in June of last year. The president was sequestered for the six days before the debate at Camp David, where, according to aides, he developed a bad cold.

Now, a year after the elder Mr. Biden withdrew from the race under pressure, the chairman of the Oversight Committee, Congressman James Comer, is investigating White House staff to see if they were governing without the president’s knowledge or consent. 

The official purpose of the probe is to review potential legislative fixes to the 25th Amendment, which lays out procedures for how to govern the country if the president becomes incapacitated. Some Democratic leaders have called the investigation a smear campaign against the Biden family. Other Democrats, on a back foot amid a drumbeat of post-election disclosures about the elder Mr. Biden’s mental acuity, have struggled to respond. 

Mr. Comer tells the Sun that the accusations that the then-president was taking Ambien — a powerful sleep aid and Schedule IV narcotic that can have dangerous side effects — adds a new dimension to the Republicans’ investigation. 

Previously the main focus of their investigation has been the White House staff’s use of the autopen — which Biden staffers used to sign a large number of official documents —  and whether Mr. Biden was aware of official actions being authorized with his autopenned signature.

“Remember: This isn’t an investigation about whether or not it’s legal to use the autopen,” Mr. Comer told the Sun on Tuesday. “This is an investigation of whether or not Joe Biden even knew what they were doing.”

Mr. Comer referenced a recent New York Times telephone interview with the former president and his staff in which the elder Mr. Biden claimed that he was aware of all decisions made that involved an autopen, including the issuing of pardons. Records reviewed by the Times, however, found that Chief of Staff Jeff Zients personally approved a number of pardons based on criteria set forth by Mr. Biden, though the president himself did not sign off on every single name. 

“Joe Biden gave an interview a few days ago and admitted [that] he had no idea who he was pardoning — that he delegated that to staff,” Mr. Comer told the Sun on Tuesday. “Then Hunter gave an interview and said his dad was on Ambien. That’s a controlled substance. Was that the first time he took Ambien? Was he a regular user of Ambien?”

Mr. Comer has been hauling members of Mr. Biden’s inner circle — a coterie of aides deeply loyal to him or to first lady Jill Biden — before his committee, one by one, to answer questions about whether or not they were aware of the president’s deteriorated physical and mental state, or if they were asked to lie about it. 

Mr. Comer told the Sun on Tuesday that he will call members of the Biden family before his committee if they are “implicated” in the use of the autopen, or in the president’s use of sedative drugs during his time in the White House. 

“If family members are implicated as to who was calling the shots at the White House,” they would be called in, Mr. Comer told the Sun. 

Nearly all of the aides who have so far been called before the committee for depositions — including Mr. Biden’s personal physician — have invoked their Fifth Amendment right against self-incrimination in order to avoid answering questions. 

Mr. Biden’s first chief of staff, Ron Klain, will testify before the Oversight Committee on Thursday. Because he is coming in voluntarily, unlike the other staffers who were subpoenaed, Mr. Klain — who was deeply involved in debate preparations — does not have the right to invoke the Fifth Amendment, Mr. Comer says.