The 2020 William Howard Taft Lecture’s focus on the per se concept in Sherman Act Section One antitrust cases came at a timely point given the recent interest in antitrust jurisprudence. This Comment looks at perspectives from each of the three branches of government in the development of current per se practice in criminal prosecutions, tracing from the sparse legislative text through the convoluted judicial history of per se illegality to its current use by the Antitrust Division of the Department of Justice in criminal cases. Recognizing that much of the development occurred in the context of a misdemeanor statute and before clarity on relevant constitutional requirements, I demonstrate that the Constitution proscribes the current use of per se illegality in criminal cases because—in the guise of a presumption of illegality—the per se concept substitutes judicial fact-finding using ever-changing and difficult-to-apply standards for factfinding by a jury in derogation of the right to trial by jury, the separation of powers, and various aspects of the right to due process. I then show how each branch of government could remedy the current infirmity and warn of the potential to lose all ability to apply the Sherman Act criminally given the vague text and interpretations based on administrative convenience.