Former White House chief of staff Jeff Zients testified behind closed doors at length about former President Joe Biden’s aging throughout the course of his term, including how he pushed Biden’s doctor to conduct a full medical workup, according to a person familiar with the transcribed interview.

Zients told House Oversight Committee investigators on Thursday that Biden’s decision-making slowed during the course of his tenure and that the former president’s difficulty remembering dates and names worsened over time, the person told CNN.

The interview was part of the Republican-led panel’s ongoing investigation into the former president’s potential cognitive decline and possible efforts to conceal it from the public. Investigators have spoken to a number of Biden’s closest former aides in recent months as part of the probe.

After Biden’s disastrous debate performance last year, Zients shared that he recommended Biden’s doctor, Dr. Kevin O’Connor, conduct a full medical workup, including a cognitive exam, and O’Connor said he would take the suggestion under advisement, the person familiar said.

Zients declined to comment to CNN on the testimony.

O’Connor declined to answer questions during his deposition in front of the committee in July.

Ahead of the debate, Zients, according to the person familiar with his testimony, said Biden had a cold but had never observed him act the way he did on stage, including “mental freezes.”

Following the debate, Zients testified, he and other Biden advisers believed that Biden should exit the race, according to the person familiar.

Former first lady Jill Biden spoke with Zients about ensuring the then president got more rest and was not overscheduled, the person said of Zients’ testimony. A separate source told CNN that conversation occurred in 2023.

Zients also shared that he discussed Biden’s age issues with other former aides whom the House Oversight Committee has interviewed, including Annie Tomasini and Anthony Bernal, who both invoked their Fifth Amendment rights and declined to answer questions in their separate interviews, the first person said.

The second source told CNN that Zients made clear in his testimony that he saw his job as ensuring that Biden met with a range of advisers to thoroughly consider issues so that he could make the best decisions, but ultimately Biden made the final decisions alone.

Zients also articulated that he had full confidence in Biden’s ability to serve as president, the second source said.(CNN)