() A longtime aide to former President Joe Biden is expected to testify in front of the House Oversight Committee on Thursday over allegations of a cover-up involving his mental acuity and use of an autopen.

Anita Dunn served as senior adviser for communications during Biden’s term. Like other former White House officials, she’ll face questions about Biden’s mental state in the final months of his tenure.

The Republican chairman of the committee overseeing the investigation, Rep. James Comer, R-K.Y., told that Dunn’s proximity to Biden could provide crucial information.

“These insiders that we’re bringing on on the autopen investigation, they were the only ones that had access to Joe Biden for more than a photo-op amount of time,” Comer said Wednesday. “And that’s why we’re bringing them in.”

Dunn could potentially plead the Fifth Amendment on Thursday, a route taken by at least three other witnesses in the probe.

Biden’s deputy chief of staff Annie Tomasini, former White House physician Dr. Kevin O’Connor and Jill Biden’s chief of staff Anthony Bernal previously invoked the Fifth instead of testifying.

Others, like former White House chief of staff Ron Klain, voluntarily answered questions about the investigation. Steve Ricchetti, once a top adviser, said Biden was fully capable of performing his job as president and said there was no conspiracy to hide his mental condition.

“I believe it is important to forcefully rebut this false narrative about the Biden presidency and our role in it,” Ricchetti said.

There are at least four additional depositions on deck in the coming months, featuring testimony from Ian Sams, former special assistant to Biden; Andrew Bates, former deputy assistant to Biden; Karine Jean Pierre, former White House press secretary; and Jeff Zients, former White House chief of staff.

Comer has not ruled out a subpoena for former Vice President Kamala Harris.

‘s Anna Kutz contributed to this report.