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The House panel investigating Benghazi will question two of former Secretary of State Hillary Clinton's top aides

Panel Republicans denied a request from former Clinton chief of staff Cheryl Mills to make her testimony in public

Washington CNN —  

The House panel investigating the fatal 2012 Benghazi attack is set to interrogate two of then-Secretary of Hillary Clinton’s top aides this week: former chief-of-staff Cheryl Mills on Thursday and former top aide Jake Sullivan on Friday.

Ahead of the closed-door hearings, tensions run high.

A source close to Mills told CNN Wednesday that Mills requested that her full testimony take place publicly – amid fears that Republicans will selectively leak bits and pieces – was denied.

Some members of the panel, including Chairman Trey Gowdy, a South Carolina Republican, are returning early from their summer recess to participate in the private interrogations.

Committee sources tell CNN that Mills will likely be asked about internal communications between Clinton and top staff, the development of talking points for then-U.S. Ambassador to the United Nations Susan Rice and any arrangements Mills had with Clinton regarding her private email server.

The committee, sources say, is not only looking into what was happening during the Sept. 11, 2012 attack and immediately afterward, but also the decision to invade Libya and its involvement in the war-torn nation after the death of leader Moammar Ghadafi.

Clinton is set to testify before the committee October 22.

While Clinton’s use of a private email address and server to conduct State Department business has not been a central focus of the panel, Gowdy has said the arrangement raises serious questions about whether the former secretary has handed over all of her Benghazi-related emails.

Committee investigators are expected to take a broader look into Sullivan’s role developing the administration’s handling of Libya, but will also likely drill down on an August 2011 memo where he outlined how Clinton should play up her handling of Libya.

A Democratic source on the committee expressed concerns that Republicans have veered away from investigating the attack itself into turning into a hit on Clinton, as she pursues the White House.

“Our concern is that Republicans’ obsession with derailing her presidential bid has shelved much of the (committee’s) core work about the Benghazi attack,” the Democratic source said. “For example, the committee has abandoned its plan to have 11 hearings this year, and it hasn’t held a single hearing since January – eight months ago. The committee was supposed to have hearings with (Defense Department) and the intelligence agencies, but we never had them.”