By Richard Lardner, The Associated Press

WASHINGTON — Two employees from Platte River Networks, the Denver-based company that hosted a private e-mail server for Hillary Clinton, refused to answer questions Tuesday after being summoned to testify before a congressional panel investigating electronic record keeping by the former U.S. secretary of state.

Bill Thornton and Paul Combetta invoked their constitutional right not to testify when they appeared before the U.S. House Oversight and Government Reform Committee; they were later excused from the session. Attorney Kenneth Eichner declined to comment when asked why he advised his clients not to answer questions.

A third witness also did not cooperate.

Bryan Pagliano, the former State Department computer specialist tasked with setting up Clinton’s server, did not attend the Republican-led hearing. His attorney said in a letter to the chairman of the Oversight and Government Reform Committee that Pagliano will continue to assert his constitutional right not to testify.

In June 2013, after Clinton had left office, the server was moved from her Chappaqua, N.Y., home to a data center in northern New Jersey, where it was maintained by Platte River Networks.

Congressional Republicans last month issued subpoenas to Platte River Networks and two other companies — Datto Inc. and SECNAP Network Security Corp. — after they declined to voluntarily answer questions to determine whether Clinton’s private server met government standards for record-keeping and security.

Pagliano spoke previously to the FBI under immunity, telling the bureau there were no successful security breaches of the server. But he said he was aware of many failed login attempts that he described as “brute force attacks.”

Pagliano also refused to answer questions last year before a House panel investigating the deadly 2012 attacks in Benghazi, Libya.

The e-mail issue has shadowed Clinton’s candidacy, and Republicans have been steadfast in focusing on her use of a private server for government business, with several high-profile hearings leading up to the election. Democrats insist the sole purpose of the hearings is to undermine Clinton’s bid for the presidency.

“I believe this committee is abusing taxpayer dollars and the authority of Congress in an astonishing onslaught of political attacks to damage Secretary Clinton’s campaign for president,” said Rep. Elijah Cummings of Maryland, the committee’s top Democrat.

The committee’s chairman, Rep. Jason Chaffetz, R-Utah, said there will be consequences for Pagliano’s refusal to appear and for “thumbing his nose at Congress.”

He didn’t specify what the penalties would be but said, “We’re not letting go of this.”

Although he doesn’t serve on the oversight committee, U.S. Rep. Ed Perlmutter, D-Arvada, attended the hearing and watched from the crowd.

He left alongside Combetta and Thornton, and afterward said he wanted to watch because Platte River Networks is a Colorado company and because there’s a chance the e-mail issue soon will be examined by the science committee, of which he’s a member.

“Potentially these guys are going to come to the science committee, so I wanted to see how it operated here in the oversight committee and if the same questions are going to be proposed in the science committee,” Perlmutter said.

Mark K. Matthews contributed to this report.