This is just a suppose: a prosecutor running for office states, “I’m not going to go after bad cop, because I need cops in general when, I prosecute rapist. If the feds pick it up fine. But, I won’t do it”
Does the guy get your vote?
(1) the term "bad cop" is subjective.
(2) Rape is not the same as assault. A cop might have reason to assault someone in the duty as a cop; this would never be true of rape. In most cases of police brutality the prosecutor might have trouble getting the police department to gather evidence.
Les