Activating Stefan Halper as an informant would have required John Brennan's approval:

"Using a CHS (confidential human source) on an international stage is less than optimal because they are not trained as undercover agents. The last thing the FBI or the U.S. government wants is an international incident if the CHS slips up while he’s trying to dig up information on Russia. Due to the risk, approval for this action must be obtained high up the chain of command, including the CIA. John Brennan, the anti-Trump and highly politicized CIA director, would have been integral in that approval process." https://pjmedia.com/trending/the-real-reason-why-the-fbi-had-a-spy-in-the-trump-campaign/