could someone please explain how politicians persucute people through the court system or how overzealous policemen prosecute people? I can see how a zealous, even overzealous proecuting attorney can go after people once the grand jury has their say but everytime I hear "why don't they just enforce the laws that are already on the books?" I cringe.
I think a good argument can be made that "selective enforcement" can be considered "persecution". If a traffic cop routinely issues citations to speeders driving Fords, while giving warnings to those speeders driving Chevys, than I don't think it's a stretch to say that the Ford drivers are being persecuted. Yes, the Ford drivers "earned" their citations, but when there's another group committing the same crimes and being given a pass, something's not right.
Police officers are the first gatekeepers to the legal system, and often have discretion as to whether someone enters the "legal machine" or walks away. District attorneys have similar discretion - while the grand jury does have a say, the quote that a district attorney could "get them [a grand jury] to indict a ham sandwich" isn't completely facetious. So now you have another group acting as a valve to decide who walks and who goes further into the machine.
And no one is operating in a vacuum - politicians can exert pressure on both the law enforcement agencies and the members of the legal system when it comes to setting priorities for what types of crime are pursued more vigorously than others.