Criminal law enforcement is traditionally considered a core executive power. Yet federal district judges exercise this power tens of thousands of times a year by initiating proceedings to revoke probation and supervised release. “Prosecutors in robes” is an insult sometimes levied by criminal defense attorneys against judges who are allegedly biased in favor of the government. In this Article, however, I do not use the phrase to suggest that district judges are acting in bad faith. Instead, I mean it literally. When judges initiate revocation proceedings, they wield a prosecutor’s power to enforce criminal law.

Drawing from the Constitution’s text and structure, early practice, and a modern empirical analysis, I argue that judge-initiated revocation violates the form and function of the separation of powers. Formally, the initiation of a revocation proceeding is a form of criminal law enforcement, which is a power that the Constitution vests solely in the President. Moreover, criminal law enforcement was originally understood as an executive power. Functionally, my empirical analysis of federal sentencing data shows that initiating revocations aggrandizes the judiciary’s role in the criminal justice system by weakening democratic accountability, undermining uniform policy, and compromising judicial impartiality.

While most legal scholars believe that a strong and independent judiciary is necessary to check prosecutorial overreach, I argue that judge-initiated revocation transforms federal district judges into “prosecutors in robes,” who themselves must be checked by the executive branch. To restore the separation of powers to the criminal justice system, only prosecutors should be allowed to initiate revocation proceedings, while judges should be limited to adjudication and sentencing. This change would ensure that no single branch of government enjoys total authority to impose criminal punishment. Our Constitution separates powers to protect liberty and prevent tyranny. A prosecutor in a robe is a king.