Well, let's look at what Rush said:
Now, when you have a CIA director for Obama praising a special counsel, then you know that this idea that Mueller is this straight arrow down the middle moderate, goes both way, is not specifically partisan. You know that’s bunk. I mean, if these people are gonna be praising the guy. Brennan also said that if Mueller is fired, I hope our elected reps will stand up and say enough is enough.
...
The opposition to Trump is fueled by this hatred — and it’s causing them, I believe, to lose elements of their sanity. I think it’s causing them to certainly lose elements of their rationality. So I wouldn’t doubt… I have no evidence, by the way. I will openly state I’m just speculating using intelligence guided by experience that these people are so far gone over what’s happened to their precious town — to their precious power base, to their precious control of things. That I wouldn’t doubt if a couple of them are making phone calls retired generals (who still get up and put the uniform on every day even though they’re retired) and soliciting their assistance — should it ever become necessary, of course — to lead a rebellion.
I don’t have any evidence of it. None whatsoever. As I say, intelligence guided by experience. But clearly there’s an uncontrolled rage and an irrationality in the anti-Trump forces — on the left primarily. The Never Trumpers are not as far gone as the leftist groups that hate Trump. So I’m not including the… I don’t think, for example, anybody at one of your favorite conservative blog sites is colluding with retired generals and colluding with Brennan and former Obama intelligence types. But I think that these people are so, so unhinged now that, in their minds, “Whatever it takes! Whatever it takes, Mabel!”
So, basically, it's an unfounded conspiracy theory Rush admits he just made up.
