Since the law is mandated by politicians, politics of course influences all aspects of the law, and criminal justice in particular, to a huge degree. And since politicians are influenced by all manner of factors, including the media, their constituents, donors, business, and lobbyists, the criminal justice system is influenced by all those factors too.
This influence affects the criminal justice system at every level. Let's take a closer look:
How Key Decision Makers are Selected
Key decision makers in the criminal justice system in particular refers to judges. Such key decision makers can be put in position either through an election, or by being appointed to the position. Either way, politics very much comes into play.
If the position is being filled in a state where voters choose to elect judges, then campaign financing becomes a factor. Plus as campaigning for election can be influenced by populism, giving the impression of doing the right thing, rather than necessarily doing the right thing, may influence the process to a huge degree.
If a judge is appointed rather than elected, however, this is done by the governor at a state level, and political points definitely come in to play – sometimes more than their ability to do the job.
At a federal level, judges are appointed by the president and then confirmed by the senate. And, of course at that level of politics, the political machine is impossible to avoid for those who want their careers to progress.
How the Creation of Laws is Politicized
State legislator and congressional representatives have a huge impact on the creation or amendment of laws. And since they're politically driven, with party affiliations, and with often grand standing for the public, how they work to create and manage laws is not always in the best interest of the country as a whole, but can be for their own political interests.
This can become particularly notable during periods of media hysteria and in the run up to elections as politicians crave to get positive media mentions.
How Prosecutors Become Political Animals
Since prosecutors are elected in many states, this by necessity to their career means they become heavily involved in politics. And although attorneys at a federal level are appointed, this can still mean their desires may be overridden by a need to tow a political line, to ensure their re-appointment.
Since, as in all things political, the current position is a temporary landing spot before moving up to the next stage of their career, political considerations can so often take prevalence over the concerns of impartial justice.
Judges and Political Influence
Although it's the job of judges to be impartial, the truth is that political motivations can influence their ability to make impartial decisions. Political opponents may use certain decisions a candidate has made against them when it next comes time for the judge to be elected. They may even attack opponents in the media in an attempt to unseat them from their position.
So a seat as a judge isn't set in stone, and on certain issues can attract a lot of political heat. Of particular concern from the media and from politicians is the appearance of being soft on crime. Even less emotive and more business related issues, such as the overlap of real estate and criminal law can surprisingly fall under political influence.
Members of parole boards are appointed by governors, and so the decisions of people on parole boards reflect on the governor. This can mean in certain circumstances there's pressure from the governor for certain decisions to be made. Whether it might not be explicitly stated, it might be an implicit understanding. And again it comes back to being tough on crime, and this being a politically safer approach than perhaps more liberal decisions.
If a felon is paroled and later re-offends in a serious way, particularly if this is mentioned in the media, this can bring a lot of political pressure on the parole board, and by extension the governor.
So since the criminal justice system is run by politicians, or appointees that were either voted in or assigned by politicians, politics has a vast influence on how the law is applied.
UPDATE 12/14/15 12:41 PM PT:
Edited to delete spam—new strategy in evidence—and user banned.