(Hanging in my posting queue for some considerable time, but just as relevant now as then.
From John McIntyre on Facebook on 9/6/18:
Guardian writer refers to a “secret cabal” in the Trump administration. What other kind does he think there is?
The crucial point is the definition of cabal. From NOAD:
noun cabal: a secret political clique or faction: a cabal of dissidents.
That is, cabals are by definition secret, and secret cabal is pleonastic, so is to be avoided (in favor of plain cabal). The general principle is the Strunk / White Avoid Needless Words dictum. (Yes, we can dispute the applicability of the dictum in particular cases. More below.)
In my mental filing cabinet, the relevant drawer is labeled pilotless drone, after a specific example I discussed at some length back in 2007. Then, of course, the question will be whether my treatment of pilotless drones carries over to secret cabals