I don't see how one gungho cop run amok makes Guiliani a bad mayor or his policies bad. You're talking about isolated incidents not the overall effectiveness of his policies.
It has nothing to do with Mayor Giuliani, the phrase was contrived as propaganda to associate bad cops behavior with the Mayor. Mayor of Baltimore is black yet I don't see anyone making the same association with bad cop behavior in that city, except when they were told to stand down during the riots.
