House Oversight Committee Chairman James Comer (R-KY) suggested he might subpoena former President Joe Biden, former first lady Jill Biden, and former chief of staff Ron Klain as the House investigates the former president’s autopen use.

Five former Biden aides are facing subpoena threats ahead of a Thursday evening deadline to comply with the House Oversight Committee’s investigation into the former president’s use of an autopen, a machine that allows anyone to duplicate the president’s signature with their authorization. The committee will determine whether Biden was, as Comer put it on Fox News’s Hannity on Wednesday night, “mentally sharp” enough to authorize the use of the device. Biden has come under increased scrutiny for his declining mental acuity during his time in office.