A Republican lawmaker is expanding investigation into the physical and mental decline of former President Joe Biden during his tenure and seeks testimony from Biden's closest advisers, including his first chief of staff.

Rep. James Comer, Republican of Kentucky, sent a letter to the former president’s closest aides on Wednesday and asked them to answer questions about Biden’s “mental and physical teacher” when he led the country.

Aides include former Biden chief of staff, Ron Klain, and members of his inner circle - consultants Michael Donilon, Bruce Reed, Steve Richetti and Anita Dunn. They did not respond to requests for comment.

A spokesman told CBS News that the committee has been in discussions with four other former White House aides (Anthony Bernal, Annie Tomasini, Ashley Williams and Biden’s physician Dr. Kevin O'Connor) to provide testimony.

After the 82-year-old’s revelation, Biden’s health scrutiny has intensified the He was diagnosed Have a positive form Prostate cancera new book claims that Biden’s White House officials have masked a “sharp decline” in his physical and mental health during his tenure.

Klain left the White House in February 2023 and also helped Biden prepare for his performance in disastrous debate in June last year. In a text message to Politico, he attributed Biden's poor performance to his advisers, who "segregated him from domestic politics."

In his letter sent Wednesday, Comer asked his assistant to appear before the committee's transcription interview committee in mid-July.

"If White House staff adopt a strategy that lasts months or even years to cover up the CEO's situation, or performs duties, a legislative response may need to be considered," Kentucky Republican wrote.

As chairman of the House Oversight Committee, Comer oversaw a long-running investigation that attempts to link President Biden’s business deal with his son Hunter. This investigation eventually led to the final improvisation question Stagnated Before the vote.