As a wave of backsliding has swept across both new and established democracies, scholars have sought to identify formal and informal institutions that can act as guardrails of democracy. But while informal norms, party structures, and formal institutions such as separation of powers have all been singled out as potential bulwarks against democratic backsliding, the literature has had less to say about what role, if any, federalism might play in stopping democracies from sliding into autocracy. While some constitutional designers and scholars have argued that federalism can help to prevent the emergence of a national tyranny, most contemporary research has emphasized the damaging effects federalism can have on democracy. In this article, we assess the relationship between federalism and threats posed by national rulers, with quantitative analysis of that relationship in countries around the world and with structured, focused comparative case studies in the United States, Brazil, Venezuela, and India. Our quantitative analysis finds no systematic relationship between federalism and backsliding, while our comparative case studies support our argument that federalism is only likely to serve as a bulwark against autocratic threats posed by national rulers under a limited set of conditions.