Bryan Pagliano appeared briefly behind closed doors Thursday before a House committee investigating the deadly 2012 Benghazi attacks. He refused to answer questions, asserting his constitutional rights not to incriminate himself, committee members said.
Pagliano's lawyers said he also will refuse to testify if served with a subpoena by two Senate committees looking into the email controversy.
Clinton, the former secretary of state and front-runner for the 2016 Democratic presidential nomination, has been dogged by questions about her use of a private email account for government business.
Senate Judiciary Committee Chairman Chuck Grassley and Homeland Security and Government Affairs Committee Chairman Ron Johnson — both Republicans — have said they are considering offering Pagliano immunity from any potential prosecution in an effort to compel him to testify.
But Pagliano's lawyers said in a letter to the senators that any such offer is premature. The senators' proposal, made in a letter earlier this week, "creates the very practical risk that our client will later be said to have waived his constitutional protections," said the letter, written by lawyers Mark MacDougall, Constance O'Connor and Connor Mullin.
A copy of the letter was obtained by The Associated Press.
In a separate letter, the three lawyers accused the chairman of the House Benghazi committee of trying to bully their client by forcing Pagliano to appear before the panel and assert his Fifth Amendment rights against self-incrimination.
Forcing him to appear at a public location "can only be intended to intimidate our client, cause him personal embarrassment and foster further political controversy," the lawyers wrote in a letter to Rep. Trey Gowdy, R-S.C., chairman of the Benghazi panel.
Gowdy denied that in a letter to MacDougall and cited comments by Clinton's former chief of staff, Cheryl Mills, complimenting Gowdy and other committee members for their "professionalism and respect" during more than nine hours of closed-door testimony before the committee last week.
Rep. Elijah Cummings of Maryland, the top Democrat on the House panel, said Pagliano's testimony "has nothing to do with the Benghazi attacks and everything to do with Republicans' insatiable desire to derail Secretary Clinton's presidential bid."
Cummings said Democrats on the panel would support granting immunity to Pagliano, but Gowdy has rejected that idea.