Given Session’s seeming predilections thus far, I doubt Brennan is really panicking. It’s more like he’s on the attack.
Brennan is not concerned about Sessions as long as Sessions (and Rosenstein and Mueller) have their jobs. They are his insurance policy.
Brennan is afraid that Sessions and Rosenstein are about to be fired and that a real AG will be hired. That's when Brennan's troubles begin.
That explains Brennan's appeal to the RINO's McTurdle and Ryan, yesterday. Brennan is afraid that Trump has now gathered enough evidence against the Deep State to quell a Ryan/McConnell impeachment for obstruction threat, if Trump were to fire Rosenstein and Sessions.
Brennan is afraid that Trump is about to make the move.