Prosecutors and judges hold positions that must be impartial and fair.
For party politics to come into play corrupts the system. If a judge treats the defendants of one party differently than another, then our legal system will collapse. Prosecutors must be impartial as well.
If a prosecutor of party A lowers or refuses to charge an evidenced crime for a defendant of party A yet throws the book at a defendant of party B, we have devolved into tribalism. Since our Constitution guarantees a fair and impartial trial, the prosecutors and judges must treat all defendants equally. A politicized justice system that prosecutes the leaders of its opposition is firing the first shots of a cold civil war, which will heat up quickly.
If a judge or prosecutor later runs for a political office, it questions whether they were fair and impartial towards defendants or made decisions based on political aspirations. For this reason alone, judges and prosecutors should agree not to run for office in the future(and be legally banned from running). All public service should require a sacrifice as proof of selfless commitment. Being banned from running for future office positions should be the sacrifice judges and prosecutors make. The potential conflict of interest alone would give every person they convicted grounds for an appeal.
A further safeguard against corruption in the courts would be the establishment of a hierarchy of prosecutable offenses. Murderers should be charged before theft cases. Felony theft should be charged before misdemeanors. The resources available must be used according to a set priority schedule. Prisons should hold the most egregious offenders. Sentences cannot be stayed for more significant offenses, while lesser offenses are charged and imposed.
If a defendant is being charged with an offense while higher offenses are excused, they should have their case suspended until cases higher on the hierarchy are attended to first.
Suppose a prosecutor or judge doesn’t follow the hierarchy of prosecutable offenses. In that case, they stand to be dishonorably discharged from public service and potentially charged with defrauding the public out of their salary. They may have to repay their compensation as restitution if accused of fraud. If they release violent offenders back into society against the hierarchy, they stand to be charged as accomplices to any future violations committed by offenders who should have been incarcerated. Being a judge or prosecutor requires competence since public safety is at stake. Any malfeasance, incompetence, negligence, or corruption should have dire consequences. Only a person who enters into “public service” without intent to serve the public but themselves would fear such a system.