Bryan Pagliano, who worked for the State Department during Clinton's tenure but was also paid separately by the Clinton family to manage the private email server she used while in office, did not appear at the hearing before the House Oversight Committee despite receiving a subpoena to appear late last week.
"I will consult with counsel and my colleagues on the committee to consider a full range of options available to address Mr. Pagliano's failure to appear," committee chairman Rep. Jason Chaffetz said, later noting, "when you are served a subpoena from the United States Congress, it is not optional."
Subsequently, Pagliano was granted limited immunity by the Department of Justice to be interviewed by the FBI.
Pagliano also declined
to answer questions when subpoenaed in a Freedom of Information Act lawsuit brought by the conservative legal watchdog group Judicial Watch.
In letters to Chaffetz sent ahead of Tuesday's hearing, Pagaliano's attorney, Mark MacDougall, argued that his office was not given sufficient time to respond to the subpoena, and asserted that any call to have Pagliano appear on Capitol Hill a second time to plead the Fifth, "furthers no legislative purpose and is a transparent effort to publicly harass and humiliate our client for unvarnished political purpose."
The Clinton campaign in the past has encouraged everyone involved with the server to cooperate and answer questions, including Pagliano.
Donald Trump's campaign seized on the development.
"The fact that the individuals who maintained Hillary Clinton's secret email server pleaded the Fifth shows once again why she can't be trusted in the White House," spokesman Jason Miller said in a statement.
Two other witnesses at Tuesday's hearing appeared before the committee but also invoked their Fifth Amendment rights and refused to answer questions.
Those witnesses, Paul Combetta and Bill Thornton, worked for Platte River Networks, a company hired by the Clinton family to maintain the server.
A fourth witness -- a former aide to former President Bill Clinton -- stayed to answer questions.