Former White House Chief of Staff Jeff Zients is on Capitol Hill Thursday as the House Oversight Committee's probe into former President Joe Biden's mental acuity draws to a close.He said nothing to reporters on his way into his closed-door voluntary interview. It's expected to last from about 10 a.m. into the afternoon.Zients is the last former Biden official expected to be interviewed by the committee, which is also looking into whether the then-president was fully aware of clemency orders and other executive actions signed by autopen during the latter half of his term.Zients' comments will be of particular interest to House investigators, given his senior role in the Biden White House for most of those final two years in office.RON KLAIN DODGES REPORTERS AFTER MARATHON GRILLING IN BIDEN COVER-UP PROBEBefore that, he served as counselor to the president and White House COVID-19 response coordinator from Biden's swearing-in in January 2021 until April 2022.Perhaps most critical to the committee is Zients' reported key role in the chain of command for Biden's autopen pardons.LONGTIME BIDEN AIDE SAYS HE STOOD TO EARN UP TO $8M HAD PRESIDENT WON RE-ELECTIONIt's not uncommon for presidents to use an autopen to sign documents, and it has been used by leaders on both sides of the aisle.However, House Oversight Committee Chair James Comer, R-Ky., is questioning whether Biden was really handing down those decisions, given public concerns about his mental and physical acuity that arose toward the end of his term.The New York Times reported that Zients would have been among the top aides relaying Biden's clemency decisions to assistants, who then drafted those orders before they were circulated back to Biden's senior officials and then later given final approval.In that same report, Biden said he made every clemency decision on his own.Axios reported earlier this month that Zients signed off on pardons granted to five of Biden's family members less than 24 hours before he left office.The former president's allies have pushed back on the Republican-led House Oversight probe, however, denouncing the investigation as politically motivated."You managed a White House in disarray after public reporting began to focus on the apparent decline of President Bidens mental capabilities. You reportedly called an all-staff call in July 2024 in which [you] urged President Bidens team to unite and move forward from Bidens terrible debate performance[.]," Comer wrote in a June letter to Zients."The scope of your responsibilities both official and otherwise and personal interactions within the Oval Office cannot go without investigation. If White House staff carried out a strategy lasting months or even years to hide the chief executives condition or to perform his duties Congress may need to consider a legislative response."