When eighteenth-century revolutionary elites set about designing new political orders, they drew on commonplace theoretical understandings of “democracy” as highly undesirable. They therefore designed government institutions in which popular participation was to be extremely limited. The new political constructions, in both France and the United States, never worked as planned. The mobilizations of the revolutionary era did not vanish as the constitutional designers hoped. More profoundly, challenging social movements were unintentionally woven into the fabric of modern democracy due to the confluence of three processes: The legitimacy claims of democratic powerholders also legitimate protest; the institutional architecture of modern democracy, especially the allocation of office through elections, provides structural support for social movements as well; and the practices of democracy recurrently trigger politically powerful emotions that energize protest. Understanding democracy therefore demands a theory of the interplay of social movements and governing institutions from the foundational moment.