Committee chairman Trey Gowdy, R-South Carolina, downplayed recent comments from Republican lawmakers about his investigation and Clinton.
"I have told my own Republican colleagues and friends, shut up talking about things that you don't know anything about. And unless you're on the committee, you have no idea what we have done," Gowdy said Sunday on CBS' "Face the Nation."
"We still have been zeroed in on Hillary Clinton," Cummings said. "It's very unfortunate."
Gowdy said eyewitnesses to the attack are "more important" interview subjects than Clinton, and that less than 5 percent of the documents collected by the committee relate to the former secretary of state.
Also on Sunday, Cummings and Gowdy traded barbed letters over the classification of a name in an email Clinton received from confidant Sidney Blumenthal and forwarded to a colleague.
Clinton is scheduled to appear before the committee Thursday at 10 a.m. The hearing is expected to go well into the afternoon.
Gowdy said the hearing will focus on what occurred before, during and after the attacks in Benghazi. He said he cares about Clinton's private emails "only to the extent that they relate to Libya and Benghazi."
Clinton's actions surrounding the 2012 attacks and her use of a private email server are under scrutiny. She has denied doing anything illegal by using a private server during her time as secretary of state and has said she has been forthcoming about releasing all her emails.