I tend to think it's the other way around. They have isolated him enough that they can portray him as a rogue actor who orchestrated whatever happened that looks bad and once they dispense with him they will be able to say "all that spying stuff is old news, we had a bad actor and we took care of him. He wasn't tied to anyone else, just a rogue and he's gone. Time to move on, this is old news". Brennan was too high up and too connected, same with Clapper. McCabe was a second tier guy who was only at the top for a short time, so he's the most expendable because he held the title but not long enough to really be in the club.
There is some reason Wray is obfuscating, dragging his feet and outright refusing to cooperate with investigators...............