This is what H&N's said too: Brennan's "policing" the term communist. But he doesn't do anything of the sort. He's not asking what it really means but whether in this context it means anything. He says that H&N use it against "the weight and sense of acquired usage." The point is proved by the fact that you would have to _undertake_ a genealogy to get past the sedimentation of meanings that have basically accrued around the Leninist ones.
Brennan's point is not to say who can or can't use the term communist--that's totally a figment of H&N's sensitive imagination, in which all critics become potential censors with despotic agency. H&N use "communist" because they get all the symbolic credit for doing so but bear no significant risk for doing it. While H&N feel it necessary to get rid of a term like "proletariat" to designate the world historical agent (it is evidently unusable--probably the "weight and sense of acquired usage," and they couldn't possibly resignify _that_), somehow the term communist can and must be retrieved. I find that choice suspicious, whatever the use they make of "communist."
Christian