As it obviously is today, politically motivated prosecution of individuals has been a problem well before our country was founded or our constitution was established. Our founders gave citizens the ability to protect their fellow citizens who are victims of politically motivated prosecution by the way they crafted the Sixth Amendment. Anyone accused of a crime is guaranteed the right to be tried by an impartial jury.
This impartial jury has not been burdened to follow the law that was declared by the judge, usually suggested to him by the prosecutor. Today, judges instruct juries that they must follow the law that the prosecutor has chosen to charge the accused with. This instruction itself is unconstitutional, however if the counsel for the accused mentions that the jury can ignore the law he will be most likely found in contempt of court and a mistrial will probably be declared.
One of the ways of combating politically motivated prosecutions would be to make sure that the jury is free not to follow a law, especially a law that was chosen to be applied against an accused for obviously politically motivated reasons. Of course this would require a judge to tell a jury of their constitutional right to not enforce a law.
Dr. W. David Herbert