Aides to presidential candidate Hillary Rodham Clinton urged a former State Department employee who helped set up her private email server to appear before a House investigative panel, but the former staffer has said he will assert his constitutional right not to testify.

Clinton, the Democratic front-runner for the 2016 nomination, has been dogged by criticism about her use of a private email server for government business during her tenure as secretary of state, and she has struggled to explain her decision.

The response of Bryan Pagliano to a committee subpoena was unwelcome news to Clinton aides who had pressed him to be interviewed by the GOP-led panel investigating the deadly 2012 terrorist attack in Benghazi, Libya.

The aides were not authorized to publicly discuss private conversations and spoke only on condition of anonymity.

Attorneys for Pagliano sent the committee a letter Monday saying their client would not testify at a hearing planned for next week. The panel subpoenaed Pagliano last month. Pagliano was a State Department employee from 2009 to 2013 and is now a private contractor working in the department’s Bureau of Information Resource Management, according to a department official who asked not to be identified when discussing personnel matters.

Maryland Rep. Elijah Cummings, the top Democrat on the Benghazi panel, said he was not surprised that Pagliano would refuse to testify, given the “wild and unsubstantiated accusations” against Clinton.

“This investigation has turned into a (quest to) derail Hillary Clinton’s nomination by any means necessary,” Cummings said.

The special committee was established last year to investigate the Obama administration’s response to the Benghazi attacks that killed four Americans, including the U.S. ambassador to Libya. The investigation has widened in recent months to focus on Clinton’s use of a private email account and server.

Clinton has dismissed both controversies as “partisan games.” She also has said she regrets using a personal email account to conduct government business.

Nick Merrill, a spokesman for Clinton’s campaign, said in a statement Thursday that Clinton and her team “have been confident from the beginning that Clinton’s use of a personal email was allowed and that she did not send or receive anything marked classified, facts confirmed by the State Department and the inspector general” for the department.

Clinton “has made every effort to answer questions and be as helpful as possible, and has encouraged her aides, current and former, to do the same, including Bryan Pagliano,” Merrill said.

Clinton is set to testify before the Benghazi committee next month.

Clinton’s campaign chairman, John Podesta, told reporters Thursday that while Clinton has encouraged cooperation with the committee, “at the end of the day I think what’s important is to hear from Hillary herself. Let the public hear what the questions are and let them hear what her answers are.”

Meeting behind closed doors, members of the House panel questioned Cheryl Mills, Clinton’s former chief of staff, for 9 ½ hours Thursday.

Mills emerged late Thursday and stood next to Cummings and Rep. Trey Gowdy, R-S.C., the committee chairman. All three described the meeting as professional and productive. Gowdy said the session would be treated as classified and declined to answer any specific questions.

Cummings called for Gowdy and committee Republicans to release a transcript of Mills’ testimony as soon as possible, a request that appeared unlikely to be granted. No other testimony has been made public since the committee began interviews last year.

Mills, a lawyer who has worked for former President Bill Clinton, thanked Gowdy and Cummings for treating her with professional courtesy and respect. Gowdy and Cummings are also lawyers.

“Ultimately the tragedy in Benghazi was about the loss of (four) individuals dear to the State Department and dear to this country,” Mills said. “We honor them by remembering what happened and doing our best to make sure it doesn’t happen again.”

Gowdy declined to outline questions asked, but knowledgeable officials said the panel was likely to have asked Mills about her role in preparing “talking points” for administration officials following the attack on U.S. diplomatic facilities in Benghazi. Questions also focused on the private email server and how it was set up.

Jake Sullivan, another former top aide who now works on Clinton’s presidential campaign, was set to be interviewed Friday, also in closed session.

(AP)