The committee has sought for months to interview Ms. Thomas, the wife of Justice Clarence Thomas, about her involvement in efforts to overturn the 2020 election.
The former president finds himself without the power of the presidency, staring at a host of prosecutors and lawyers who have him and his associates in their sights.
As the department decides whether to appeal the ruling on a special master, it is balancing a desire to speedily resolve the inquiry with the need to limit an expansive view of executive power.