The scope of the President’s legal authority is determined in part by historical practice. This Essay aims to better understand how such practice-based law might operate as a constraint on the presidency. Some scholars have suggested that presidential authority has become “unbounded” by law, and is now governed only or primarily by politics. At the same time, there has been growing skepticism about the ability of the familiar political checks on presidential power to work in any systematic or reliable fashion. Skepticism about law’s potential to constrain in this context is heightened by the customary nature of much of what purports to be the law of presidential power, and by the limited availability of judicial review. As the Essay explain...