I don't think that McCarthy is arguing against this. Powell has argued this point, but the Court has seemingly ignored it. McCarthy is suggesting that the Court can continue to ignore it, but get to the same result, removing Sullivan from the case.
What McCarthy conveniently does is ignore the fact that the same Swamp DoJ / Court Apparatus ignored 50 people, all with the same political affiliation, lying to the FBi.
The Elephant in the room is invisible to McCarthy, who accepts that as part of the Justice System.