Driving the news: House Oversight Committee chair James Comer (R-Ky.) sent letters to Biden's personal physician, Kevin O'Connor, and former White House officials Neera Tanden, Anthony Bernal, Annie Tomasini and Ashley Williams seeking testimony.

While House Republicans and Trump appear to be aligned in their desire to investigate Biden’s fitness to serve, there is some frustration brewing among congressional committees about how quickly the Trump administration is responding to some of their requests, according to multiple GOP congressional sources familiar with the matter.

The GOP-led House Committee on Oversight and Government Reform has called on President Joe Biden's physician and former White House aides to sit for interviews as it investigates.