In the wake of former President Trump’s two impeachments, the integrity of the Constitution’s separation of powers and, in particular, accountability for wrongdoing in the White House short of a presidential election is legitimately in question. Yet to date, there has been no thorough scholarly analysis of the source of law underpinnings of the virtually universally accepted aphorism that “a sitting president cannot be indicted” and is thus immune from judicial oversight for criminal wrongdoing. That apothegm derives from two memoranda produced by lawyers for Richard Nixon and Bill Clinton during periods in which their respective presidencies were in crisis. This Article asks the question: What is an OLC memo as a source of law? It applies constitutional and administrative law principles to conclude that, considered together, these particular OLC memos either constitute a categorical prosecutorial declination determination within the ambit of the president’s Take Care prerogative or a non-legislative rule within the meaning of the Administrative Procedure Act.