Josh Campbell is a CNN Law Enforcement Analyst, providing insight on crime, justice and national security issues. He previously served as a supervisory special agent with the FBI, and worked on an FBI team responsible for investigating terrorist attacks and kidnappings overseas. Follow him on Twitter at @joshscampbell. The views expressed in this commentary are his own.

(CNN) In a battle involving important principles of separation of powers, House Intelligence Committee Chairman Devin Nunes is fighting with the Justice Department, whose leaders have rejected his demands to turn over intelligence connected with special counsel Robert Mueller's investigation into Russian interference in the 2016 election.

Josh Campbell

While details remain murky, the issue is whether Congress should be able to demand personal information about a secret intelligence source assisting Mueller's efforts. According to The Washington Post , Nunes issued a subpoena to DOJ demanding "all documents referring or related to the individual." This appears to contradict his original claim that he only sought access to information, and nothing regarding a specific person.

Both these things cannot be true. And why is Nunes blurring the lines of congressional oversight and inappropriately asking for evidentiary information in the middle of a sensitive special counsel investigation?

Those of us who have recruited and handled human sources around the world understand the gravity of exposing people who risk their lives to provide intelligence necessary for defending the nation. The relationship between a human source and the government is based on trust -- trust that the handling officer will keep the source's identity secret and not disclose the information they provide to anyone without a need to know, especially loose-lipped politicians.

Although Congress has a vital oversight role, enshrined in the founding of the House Iintelligence Committee in 1977 after gross civil liberties abuses by government agencies, those same agencies would be correct to question the motives of Nunes, who has proved time and again that he is not above politicizing intelligence agencies for partisan gain.

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