This Article takes United States v. Texas, a case about the legality of President Obama’s “Deferred Action for Parents of Americans” (DAPA) immigration initiative, as an entry point for analyzing a significant and publically-salient, yet undertheorized, problem in constitutional law: executive discretion in enforcing the law. Although Republican and Democratic administration alike have long asserted a constitutionally-inherent power to decline to enforce civil and criminal laws, former-President Obama’s recent high profile exercises of this authority, including his enforcement policy on federal marijuana law and immigration law, have led to increased attention to enforcement discretion among popular and scholarly commentators. Surprisingly, however, academic commentators have almost completely ignored the relevance of a canonical separation of powers precedent to the constitutional debate surrounding executive nonenforcement: Youngstown Sheet & Tube Co. v. Sawyer. This Article is the first to systematically apply Justice Jackson’s famous Youngstown concurrence to the puzzle of the executive’s constitutional discretion in law enforcement. By doing so, the Essay provides a common lexicon within which commentators can debate the constitutionality of presidential nonenforcement in particular contexts, including DAPA. The Article's second contribution is to offer a positive theory of constitutionally-inherent enforcement discretion, including the power to supervise and prioritize law enforcement activities. I derive this theory from constitutional text, including the Executive Power Clause, the Take Care Clause, and the Due Process Clause. This inherent power, however, is malleable and defeasible rather than fixed and absolute. Congress can either explicitly or implicitly confer executive enforcement discretion to the constitutional maximum (Youngstown Category 1). Likewise, Congress can explicitly or implicitly cabin executive enforcement discretion, reducing it to the constitutional minimum (Youngstown Category 3). When the Executive is faced with Congressional silence, he acts in Youngstown Category 2. In the second category’s “zone of twilight,” however, executive enforcement discretion is limited to the President’s inherent constitutional powers. Based on my positive theory of constitutionally-sanctioned enforcement discretion, I argue that, in Category 2, the Take Care Clause does not preclude the Executive from exercising enforcement discretion, including the power to coordinate categorical enforcement priorities. Finally, I argue that, even in Category 3, the President’s inherent power of enforcement discretion ensures that he always retains at least some discretion to decline enforcement in individual cases, especially in the criminal context. Furthermore, in light of the powers concomitant to his constitutional duty to supervise, including the power to coordinate and prioritize enforcement, I argue offer a novel argument that the President’s inherent enforcement discretion power may extend beyond individualized discretion to countenance the creation of categorical civil enforcement priorities, even in Category 3. The Article concludes by applying the Youngstown framework and my positive theory of executive enforcement discretion to the question whether DAPA violates the Constitution. I conclude that DAPA most comfortably falls in Category 2, and that its provisions do not exceed the Executive’s inherent enforcement discretion under the Constitution.