We might begin to think about some of the criteria that make prisoners in the United States politicized entities in the first place. According to the criminologists Jeff Manza and Christopher Uggen, prisoners have become objects of political consideration because they are directly tied to public passions and outrage, as well as the mobilization of this outrage by political elites. Over the past thirty years, the US justice system has developed an unusually harsh system of punishment for criminal offenders. Slogans like “tough on crime” and the “war on drugs” have galvanized the public precisely because they touch upon fears that most Americans feel intricately connected to. Democratic lawmakers, for example, campaigned in favor of mandatory minimum sentences for drug offenses in 1986. By using a kind of rhetoric that played directly into the concerns of citizens about the spread of violence, poverty, and gang-related activity, these politicians used prisoner sentences as an effective political tool.
You might also consider the arguments put forward by the French philosopher and critical theorist Michel Foucault. In Discipline and Punish, Foucault asserted that the power in the social sphere which manifested in criminal behavior served as a reflection of the professional discourse that occurred outside of it. In other words, the emergence of a professionalized, political discourse of criminality directly contributed to the formation of a criminal identity in prisoners themselves. Foucault famously utilized the imagery of the panopticon to drive this point home. In the modern penitentiary, prisoners are observed on all sides by representatives of the politicized criminal discourse. Foucault says,
He who is subjected to a field of visibility, and who knows it, assumes responsibility for the constraints of power; he makes them play spontaneously upon himself; he inscribes in himself the power relation in which he simultaneously plays both roles; he becomes the principle of his own subjection.(Discipline and Punish, pg. 202–203)
What this means is that the prisoner ultimately comes to internalize his identity as a criminal, and his unconscious behavior becomes modified in order to fit this new identity. This is politically significant because it ties into questions as to whether the modern penal system is actually reformative. If we think about what Foucault is saying, it actually seems to be the opposite—that in fact the modern penitentiary is the most sophisticated state organ for creating and maintaining a category of permanent criminals.
These considerations should help you get started thinking about how and why prisoners are viewed politically.