Democratic presidential front-runner Hillary Rodham Clinton said that her family paid a State Department employee to maintain the private email server she used while secretary of state and compensated him “for a period of time” for his technical skills.

After picking up the endorsement of New Hampshire’s senior senator, Democrat Jeanne Shaheen, Clinton was again pressed to answer questions about an issue from her time in the Obama Cabinet that has dogged her presidential candidacy.

“We obviously paid for those services and did so because during a period of time we continued to need his technical assistance,” Clinton told reporters after a campaign event.

That employee, Bryan Pagliano, told a House committee last week that he would invoke his constitutional right against self-incrimination if called to testify.

In August, Clinton gave the FBI the server, kept in her suburban New York home, that she used to send, receive and store emails while secretary of state from 2009 to 2013.

Clinton has said she set up her own system, instead of using a State Department account, for the convenience of using a single hand-held email device.

Clinton told reporters she did not think the revelation about Pagliano’s payment would hurt her campaign and she encouraged “anyone who is asked to cooperate” with the committee to do so.

After a stop at a bookstore, Clinton spoke to more than 200 people at a union reception in Manchester to seek support from leading New Hampshire labor activists.

She hinted at the themes of a speech she is scheduled to give on Wednesday in Washington defending the Obama administration’s nuclear agreement with Iran, which she called “the best alternative we have.”

“Our strength should be measured in what we prevent, what good things we make happen and how we bring others to our side in dealing with some of these challenges we’re confronting,” Clinton said, referring to Iran’s nuclear program and the rise of Islamic State militants.

Republicans have seized on the email controversy and say it underscores polls which have shown large numbers of voters questioning her trustworthiness.

Some Democrats are concerned about her campaign struggles and pine for more options, and speculation about a late entrance into the presidential race by the vice-president Joe Biden has spiked in recent weeks.

She also faces an unexpectedly strong challenge from Vermont senator Bernie Sanders, a self-described democratic socialist, who is drawing large crowds to his rallies and making gains in polls of early voting states such as New Hampshire and Iowa.

Current and former Clinton aides have been testifying before the House committee investigating the deadly 2012 Benghazi attacks that killed the US ambassador to Libya and three other Americans. The committee also has delved into Clinton’s email practices at the State Department.

Thousands of pages of her emails publicly released in recent months have shown that Clinton received messages that were later determined to contain classified information, including some that contained material regarding the production and dissemination of US intelligence.

Her comments that she didn’t stop to think about setting up a private email server in her home belied the careful planning and technical sophistication required to set up, operate, maintain and protect a private server effectively — especially one responsible for the confidential communications of the US government’s top diplomat as she traveled the globe.

Even homebrew servers typically require careful configuration, Internet registration, data backups, regular security audits and a secondary power supply in case of electrical problems.

But Clinton reiterated that she did not “send or receive any material marked classified. We dealt with classified material on a totally different system. I dealt with it in person.”

She is scheduled to testify next month.