Within the American system of shared power among institutions, the executive branch has played an increasingly prominent policy role relative to Congress. The vast administrative discretion wielded by the executive branch has elevated the power of the president. Republican and Democratic presidents alike have employed an arsenal of administrative tools to pursue their policy goals: high-level appointments, administrative rule making, executive orders, proclamations, memoranda, guidance documents, directives, dear colleague letters, signing statements, reorganizations, funding decisions, and more. Presidents Obama and Trump employed most of these tools in an effort to shape the implementation and outcomes of the Affordable Care Act (ACA) during its first decade. This article focuses on the Obama and Trump administrations' use comprehensive waivers to shape ACA implementation. The Obama administration had mixed success using waivers to convince Republican states to expand Medicaid. Compared to Obama, the Trump administration has found it harder to accomplish its policy goals through waivers, but if the courts support the Trump administration's work requirement and 1332 waiver initiatives, it would enable the president to use waivers to achieve an ever broader set of goals, including program retrenchment.