House Intelligence Committee Chairman Adam Schiff looks on during a news conference Wednesday held along with House Speaker Nancy Pelosi. Tom Brenner/Getty Images

While three committees — Intelligence, Foreign Affairs, and Oversight — are involved in today’s deposition, the Intelligence Committee staff is doing the questioning.

Here's how a House Intelligence Committee aide put it:

“Consistent with the Speaker’s designation of the HPSCI (House Permanent Select Committee on Intelligence) as the lead committee conducting the House’s impeachment inquiry, Thursday’s interview will be conducted by HPSCI staff. In preparation for this interview, HPSCI investigators have been working with the Committee on Foreign Affairs and the Committee on Oversight and Reform, both of which will have equal Majority and Minority representation."

How Republicans are reacting: Yesterday, Rep. Michael McCaul, the top Republican on the Foreign Affairs Committee, said he protesting the move by Democrats to let the House Intel Committee take the lead in questioning Kurt Volker today.

McCaul wrote: “I was alarmed to learn – less than 24 hours before the first interview is scheduled to start – that it will be led by the Intelligence Committee and that questioning will be done solely by their staff. Also we were told that only a single Republican professional staffer from the Foreign Affairs Committee will be allowed to attend while the majority will have two. These constraints on committee and Republican participation are unacceptable and at odds with House Rules and general fairness. …We demand equal representation and participation in this inquiry, there is too much at stake for America and Congress.”