Joe Biden’s White House physician on Wednesday declined to answer questions during a closed-door deposition with the House Oversight Committee, invoking his Fifth Amendment right as the Republican-led panel pushes forward in its probe of the former president’s mental fitness and decline.

While Dr. Kevin O’Connor appeared on Capitol Hill Wednesday, his attorneys said he “respectfully declined to answer any questions” from the panel, which had refused to limit the scope of the interview – imperiling, they said, his physician-patient privilege.

“Revealing confidential patient information would violate the most fundamental ethical duty of a physician, could result in revocation of Dr. O’Connor’s medical license, and would subject Dr. O’Connor to potential civil liability. Dr. O’Connor will not violate his oath of confidentiality to any of his patients, including President Biden,” O’Connor’s attorneys said in a statement on his behalf.

The investigation is the latest front in the GOP push to expose alleged cover-ups by Biden and his inner circle that had fallen dormant in the last Congress. Republicans say the interviews are critical to supporting claims of the former president’s cognitive decline in the final days of his administration. Democrats, meanwhile, have dismissed the probe in its entirety as a political stunt.

The panel subpoenaed O’Connor in June after first seeking a voluntary interview, and has requested interviews with nearly a dozen former White House aides in recent months. But the interviews, which began as voluntary appearances, have grown increasingly contentious after President Donald Trump waived executive privilege for the physician and others.

O’Connor’s team on Wednesday argued the panel should pause its probe until the Department of Justice concludes its separate criminal investigation into his predecessor’s actions and use of the autopen, which Trump had ordered in a memorandum.

“We believe that the Committee should hold its investigation in abeyance until any criminal investigation has concluded,” O’Connor’s team said.

A committee aide pushed back on the notion that O’Connor pleaded the Fifth Amendment because of doctor-patient privilege, arguing the physician did not answer any questions beyond his name.

Invoking the Fifth Amendment is typically done to avoid answering specific questions. Though it can be perceived by the public as a way of avoiding accountability, the US Supreme Court has long regarded the right against self-incrimination as a venerable part of the Constitution and, in legal proceedings, tried to ensure that a witness’ silence not be viewed as evidence of guilt.

Following O’Connor’s departure, House Oversight Chair James Comer accused the doctor of wanting to “conceal the truth.”

“The American people demand transparency, but Dr. O’Connor would rather conceal the truth. Dr. O’Connor took the Fifth when asked if he was told to lie about President Biden’s health and whether he was fit to be President of the United States,” the Kentucky Republican said in a statement.

The committee still has multiple interviews scheduled throughout the summer. Unable to invoke executive privilege to avoid answering questions, some witnesses have already sought to stave them off.

Former Biden aide Anthony Bernal withdrew from a voluntary interview last month after the White House counsel’s office made clear that privilege would be waived. Comer then subpoenaed Bernal for his testimony.

At least one interview has already led to a dispute over testimony.

Comer claimed that Neera Tanden, Biden’s director of the Domestic Policy Council, told the committee during her voluntary closed-door interview last month that she had “no visibility” into how the approval for Biden’s autopen signatures worked – a point that Republicans have latched onto. A Democratic committee official, however, swiftly pushed back on that characterization, saying that Tanden “repeatedly and explicitly confirmed that she received President Biden’s written sign-off on every executive action she presented him with.”

“Any other characterization is a distortion of the testimony,” the official told CNN at the time.

Interview transcripts from Tanden’s appearance have not yet been released.

The top Democrat on the House Oversight Committee, Rep. Robert Garcia of California, criticized the Republican effort, saying the GOP is more concerned with the former president’s health than their constituents’ access to health care.

“The only person’s health that Republicans care about is Joe Biden’s – even as 17 million Americans lose access to affordable health care thanks to their big budget betrayal,” Garcia said in a statement.

One Biden ally accused Republicans of playing politics with the congressional inquiry.

“It’s an attempt to smear and embarrass. And their hope is for just one tiny inconsistency between witnesses to appear so that Trump’s DOJ can prosecute his political opponents and continue his campaign of revenge,” the person told CNN.