House Republicans on Sunday demanded that President Biden’s personal physician explain whether he can provide “accurate and independent” assessments, citing his reported refusal to order a cognitive test for the 81-year-old president and other matters related to the Biden family.

The House Oversight Committee “is investigating circumstances surrounding your assessment in February of this year that ‘President Biden is a healthy, active, robust 81-year-old-male, who remains fit to successfully execute the duties of the Presidency,’” Rep. James Comer (R-Ky.) who chairs the committee, wrote in a letter on Sunday to Kevin O’Connor, the physician to the president.

Outside medical experts and some Democrats have raised questions about Biden’s cognitive health following the president’s halting performance in last month’s debate with rival Donald Trump, where Biden struggled to explain some of his key policies, stumbled through multiple answers and appeared to sometimes lose his train of thought. In the letter to O’Connor, Comer cited other reports of Biden’s recent mental lapses, such as claims that the president is sometimes confused or listless in private meetings.

Noting that O’Connor has declined interview requests from the media, Comer also asked him to sit for a transcribed interview with the Oversight Committee.

“The Committee now turns to you to provide answers regarding your independence because of the mixed and confused messaging coming from the White House regarding the President’s ability to perform his job,” Comer wrote.

The White House, which has dismissed Biden’s debate performance as an outlier and said that he remains alert and high-energy in private settings, did not immediately respond to question about whether O’Connor would testify. The GOP-led committee has previously turned to subpoenas when individuals have declined to comply with its requests to testify.

O’Connor, a retired Army colonel and a current member of the White House medical unit, has served as Biden’s personal physician since 2009. The doctor of osteopathic medicine has also treated other members of the Biden family, including the president’s son Beau Biden, who died of cancer in 2015. In his February assessment of Biden, O’Connor wrote that the president received “an extremely detailed neurological exam” that was “reassuring,” with no findings consistent with a disorder such as Parkinson’s disease.

The White House has declined to make O’Connor available for questions about his assessments of the president.

Some of O’Connor’s medical colleagues have questioned his decision not to order a cognitive test for the president.

Three of O’Connor’s former colleagues in the White House medical unit, speaking on the condition of anonymity to describe confidential relationships, told The Washington Post last week that Biden’s debate performance suggested to them that the president should undergo cognitive screening.

Ira Monka, the president of the American Osteopathic Association and a friend of O’Connor’s, also told The Post that he thinks Biden’s performance should prompt an initial cognitive review to see if more tests are needed.

In his letter, Comer also cited testimony by James Biden, the president’s brother, who told the committee that O’Connor provided him with advice as he worked with Americore Health LLC, a company that operated rural hospitals and is now going through bankruptcy proceedings.

“The Oversight Committee is concerned your medical assessments have been influenced by your private business endeavors with the Biden family,” Comer wrote, requesting that O’Connor turn over all documents in his possession related to Americore and James Biden.

The White House dismissed suggestions that O’Connor’s medical advice was influenced by any dealings with James Biden.

“Here they go again, pushing their crazy, discredited conspiracy theories,” Ian Sams, a White House spokesperson, wrote in an email. “If extreme House Republicans want to take a look at a White House physician, here’s an idea for where to start,” he added, sharing a link to an article on former White House physician and current Republican congressman Rep. Ronny Jackson (R-Tex.).

An email sent to the email address listed on Americore’s website was returned to sender. A telephone call to the phone number listed on Americore’s website went to voicemail.

Michael Kranish contributed to this report.