Republicans on Thursday plan to grill President Biden’s first chief of staff and debate preparation coach, Ron Klain, about the president’s mental acuity and the White House’s use of the autopen as a governance tool. Because Mr. Klain was not subpoenaed by the committee and is coming voluntarily, he is expected to answer questions. 

Mr. Comer says that because he is appearing for a transcribed interview voluntarily — not a deposition necessitated by a subpoena — Mr. Klain is waiving his right to invoke the Fifth Amendment and refuse to speak. Several former Biden aides have invoked the Fifth thus far. 

“He’s coming in voluntarily, so it’s my understanding you only invoke the Fifth when you are subpoenaed, so hopefully Klain will answer questions,” Mr. Comer told reporters Wednesday. He says Mr. Klain absolutely must answer the committee’s first question, which is: “Were you ever told to lie about the president’s health?”

“We’ve had three people in his inner circle plead the Fifth on that. If he can’t answer that question, my god,” the chairman said. 

Mr. Klain’s session with the Oversight Committee comes after three key White House figures who were subpoenaed by Mr. Comer took the Fifth. The White House physician, Kevin O’Connor, took the Fifth, as did Jill Biden’s chief of staff, Anthony Bernal, and Annie Tomasini, a deputy chief of staff to Mr. Biden. Mr. Bernal and Ms. Tomasini were reported to have walled off Mr. Biden from everyone but a tiny number of family members and loyal aides. The aides were known as “The Politburo,” according to a best-selling book, “Original Sin,” about Mr. Biden’s cognitive decline and the “cover-up.”

Beyond Mr. Klain, several other Biden aides are expected to come in for interviews this summer. A former White House counsel spokesman, Ian Sams, who defended Mr. Biden after the release of the Hur report describing the president as an “elderly man with a poor memory,” is among those who will appear.

Mr. Biden’s press secretary, Karine Jean-Pierre, deputy press secretary, Andrew Bates, and chief of staff, Jeff Zients, will also likely come in for interviews. 

According to a report from Politico, Mr. Biden’s longest-serving aides, many of whom have worked for him for decades, plan to sit for interviews voluntarily in the next two weeks. Three “Politburo” mandarins —  Counselor Steve Ricchetti, Senior Advisor Mike Donilon, and Deputy Chief of Staff Bruce Reed — are slated to appear, along with Senior Advisor Anita Dunn, who wielded enormous power over messaging and communications. They will all appear before August 7.

The first Biden aide to sit for an interview with the Oversight Committee in the autopen probe was Neera Tanden, a Hillary Clinton loyalist who served as Mr. Biden’s staff secretary and senior advisor after her nomination to be budget director had to be withdrawn due to her history of polarizing comments. As staff secretary, it was Ms. Tanden’s responsibility to manage the president’s daily workflow and important documents. 

She told the panel in June that she would get orders from Mr. Biden’s inner circle — but not the president himself — to use the autopen for certain documents. In a statement after her testimony, Mr. Comer said that Ms. Tanden told lawmakers she had “minimal” interaction with the president as she was running a critical part of the West Wing operation. 

“She explained that to obtain approval for autopen signatures, she would send decision memos to members of the President’s inner circle and had no visibility of what occurred between sending the memo and receiving it back with approval,” Mr. Comer said at the time. “Her testimony raises serious questions about who was really calling the shots in the Biden White House amid the President’s obvious decline.”

On Tuesday, Mr. Comer confirmed to the Sun that he was ready to call in members of the Biden family after the former first son, Hunter Biden, claimed that his father was taking the sedative drug Ambien ahead of his disastrous June 2024 debate performance. 

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

Mr. Comer referenced a recent interview Mr. Biden did with the New York Times, during which the former president claimed that he was aware of all decisions made that involved an autopen, including his commutations and pardons. He simply set out criteria for the presidential relief, however, and his staff made the final lists of individuals receiving pardons. The autopen was also used to grant full pardons for the president’s siblings and their spouses. 

“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,” the chairman said, referencing the Times interview. “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?”