Of note - Campbell's attorney is Victoria Toensing, a former Deputy Assistant Attorney General under Reagan who is now handling the Mueller investigation for President Trump along with her husband, former federal prosecutor Joe diGenova (also of note, newly minted National Security Advisor John Bolton was Reagan's Assistant AG, presumably while Toensing was a Deputy Assistant AG in the criminal division). 

After Campbell spent decades working for the CIA, he was "turned over" to the FBI for counterintelligence work due to relationships he had forged deep within the Russian uranium industry. While deep undercover, Campbell uncovered two related bribery schemes involving Russian nuclear officials, an American trucking company, and efforts to route money to the Clinton Global Initiative (CGI) through an American lobbying firm in order to overcome regulatory hurdles, according to reports by The Hill and Circa.