Everyone without a need to know should have their clearances yanked, and Brennan has no need to know in his current role. This should be standard process as it is everywhere else and at every other level of access.
Even without need to know, they may have access through connections in one of the other 4 nations that share intelligence access with the US. https://en.wikipedia.org/wiki/Five_Eyes
“I have a security clearance and once I no longer have a need to know, it will be suspended. Period.”
I had one years ago when I worked for a military R&D company during the Vietnam war. To get it, I had to undergo an FBI investigation. My friends told me that they were contacted by the FBI. When I left the company, it was revoked, and the FBI made it very clear what my responsibilities were to protect what I knew after I left.
For 30 years, I didn’t talk about what I did. It wasn’t until a friend e-mailed me, unknowingly, about a weapon for which I was responsible, complete with pictures of a congressman waiving it around in a hearing room, that I had anything to say.
Back when Sandy Berger committed his unpunished crimes, I asked the same question about his clearance because he was obviously not part of the Bush administration. The answer was that his former boss, Bill Clinton, was the sponsor of his clearance.
Based on that, I'm going to say that Bathhouse Barry is the sponsor of Brennan and the rest of the former Obama officials who still have clearances.