The House Oversight Committee has scheduled voluntary transcribed interview with four Biden White House aides as it investigates whether there was a cover-up of President Biden’s mental state, according to a committee aide.

The confirmed interviews come as the panel has expanded the reach of its probe, asking top aides to sit with the committee’s investigative staff.

Neera Tanden, the former director of the Domestic Policy Council, will sit for an interview June 24, while Anthony Bernal, a former assistant to the president and senior adviser to the first lady, will do so June 26.

Next month, Ashley Williams, the former special assistant to the president and deputy director of Oval Office Operations, will sit with staff for a July 11 interview, while Annie Tomasini, a former assistant to the president and deputy chief of staff will appear July 18. 

Last week Committee Chair James Comer (R-Ky.) subpoenaed Biden’s White House doctor, Kevin O’Connor, for a deposition on June 27.

The day prior, Comer sent letters demanding interviews to former chief-of-staff Ron Klain, senior adviser Anita Dunn, former counselor Steve Ricchetti, and aides Michael Donilon and Bruce Reed. 

“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 executive’s condition or to perform his duties Congress may need to consider a legislative response,” Comer wrote in a letter to Klain. 

The White House also confirmed last week that pardon attorney Ed Martin would be reviewing Biden’s pardons for his family members, as well as some other clemencies granted during his final days in office.