State Department officials are facing a spate of new Freedom of Information Act requests for the records of key aides to Hillary Clinton from her time as secretary of state, including several who have since joined her presidential campaign.

Citizens United, a conservative watchdog group, filed six FOIA requests on Jan. 15 that drilled down on four State Department officials who have largely remained out of the spotlight in the discussion over Clinton's ethical conduct as the nation's chief diplomat.

"This is now a two-year investigation that we have been leading, and these are just the continuation of that investigation," David Bossie, president of Citizens United, told the Washington Examiner of the new requests. "These FOIAs are following investigative leads or threads and trying to gain more information as to how the global 'Clinton, Inc' worked."

Two of the FOIA requests sought the communications of Dennis Cheng, former deputy chief of protocol at the State Department. Cheng now serves as the national finance director of Clinton's campaign.

A longtime Clinton insider, Cheng transitioned with Clinton from her failed 2008 campaign into the State Department. He left the agency in 2011 to join the Clinton Foundation before assuming his role on the present Clinton campaign.

Bossie said Cheng has long been involved in "donor maintenance." His group requested records of Cheng's communications with the Clinton Foundation, a controversial consulting firm called Teneo Strategies and well-known Clinton aides like Cheryl Mills and Huma Abedin.

Another FOIA request sought records of communication between Capricia Marshall, Cheng's boss in the State Department protocol office, and employees of the Clinton Foundation and Teneo.

Teneo is a consulting firm founded by former Clinton aide Douglas Band that has reportedly grown from its close connections to the Clintons. The company has welcomed a number of Clinton confidantes onto its payroll, including Abedin, who consulted for Teneo while also collecting a paycheck from the State Department.

Citizens United asked for records of communication between Heather Samuelson, a liaison between the State Department and the White House, and Mills and Abedin.

The group also asked for correspondence from David Wade, former chief of staff to Secretary of State John Kerry, in an effort to gauge the extent of Wade's involvement in the Clinton email screening process.

Citizens United is presently engaged in 11 different lawsuits against the State Department over roughly 40 FOIA requests for Clinton-related records, including three cases opened within the past two weeks.

The agency has consistently dragged its feet when handling records requests for the Clinton emails. Many transparency advocates like Citizens United have discovered costly litigation is the only way to force the release of desired documents.

"Our only investigative tools are FOIA requests and the subsequent litigation that's required to get anything out of the State Department," Bossie said.

Agency officials have unleashed a variety of creative excuses against groups like Citizens United to explain their failure to search for or hand over documents.

For example, the State Department told Citizens United in a recent case that it could not provide email discussions of Clinton's schedule — even though it had produced similar records to the Associated Press in a recent, unrelated lawsuit — because the request for such emails was too broad.

State officials stuck to that argument even after the watchdog group narrowed the request to email discussions mentioning key scheduling phrases like "meeting" that were sent only in relation to Clinton's 87 foreign trips. That FOIA case will continue Feb. 9.