Scholars often try to define presidential prerogative in legal terms and thereby recognize its technical “illegality.” This article argues that prerogative cannot be seen in such simple legal terms. The author situates prerogative more explicitly in the context of Madison's constitutional framework: acceptance (or rejection) of a particular use of prerogative will hinge on the judgment of the other branches of government and not simply on the letter of the law. Prerogative cannot be neatly defined beforehand. What is accepted as a measure of prerogative at one moment may well be rejected at another. Seeing presidential prerogative in this way gives voice to Madison's dynamic constitutionalism.