By Mike Conte, Kylie Atwood and Paul LeBlanc, CNN

(CNN) -- Secretary of State Mike Pompeo's wife asked State Department staff to help send personal family Christmas cards, according to an email exchange obtained by the State Department Office of Inspector General as part of an investigation into potential misuse of taxpayer resources, a source familiar with the investigation told CNN.

The request from Susan Pompeo, which was first reported by McClatchy, was sent to State Department aide Toni Porter, who testified before the House Foreign Affairs Committee last month that she had assisted with personal Christmas cards and felt uncomfortable with the task. Porter said she did not tell anyone at State about the instance.

That testimony came as part of a probe from congressional Democrats into the ouster of State Department Inspector General Steve Linick at Pompeo's behest in May.

As part of that probe, Linick testified in early June that his office was looking into five matters of potential wrongdoing at the State Department, including potential misuse of taxpayer resources. Pompeo has repeatedly denied that Linick's ouster was retaliatory and rebuked Democratic lawmakers, including House Foreign Affairs Chairman Eliot Engel of New York, over the probe.

Pompeo defended his wife Monday evening, telling Fox News, "The fact that they're picking on my wife, who has done yeoman's work as a volunteer to try to make life better for every officer at the State Department, I find pathetic and sad."

"But we'll keep doing the right thing," he continued. "We'll keep obeying the law. We'll keep doing everything that's proper and we'll leave the State Department a better place than we found it when our time here is done."

Pompeo and his wife have also been criticized for holding so-called Madison Dinners in ceremonial rooms at the department, where government resources are used to host CEOs, GOP donors, conservative reporters and some foreign diplomats. They are viewed as dinners to build Pompeo's network and donor base, and not seen as dinners geared toward foreign policy, State Department officials involved in the planning have told CNN. The State Department has defended the events as part of Pompeo's official duties.

Susan Pompeo has been heavily involved in the planning of those dinners and the guest list, State Department officials told CNN. On Monday night, the dinners, which had been paused during the pandemic, started up again. The dinners are being investigated by congressional Democrats.

Earlier this month, the Trump administration named Matthew Klimow as the new acting State Department inspector general -- the second person to be tapped for the temporary role since Linick was ousted.

The Office of Inspector General acts as an independent watchdog of the State Department. One of its core values is "integrity."

"We maintain our independence and act with courage, honesty, and professionalism. Our work is fact-based, objective, and supported by sufficient evidence that meets professional standards," it states on its website.

A former senior State Department official previously told CNN that "an independent IG's job is to be that: independent. If the IG is doing his job, the IG is going to be at odds with the seventh floor. The IGs job is to uncover waste fraud and abuse," they said.