ABSTRACT The term “deep state” has enjoyed political prominence in recent years, especially in movements around former President Donald Trump. However, the term emerged in the activist milieu after the founding of Students for a Democratic Society, which sought to engender political realignment in the aftermath of the Kennedy assassination. Those on the far right who use the term to level accusations of conspiracy at supposed subversives in the administrative state are unwittingly drawing on a long-running but little-analyzed intellectual tradition. (...) In that tradition, conspiracy theories purport to unmask the real intentions of political actors in order to facilitate cooperation and recruitment across ideological and partisan divides. From the postwar period to the present, conspiracy theories, and the “deep state” vocabulary in particular, circulated freely across the left-right political divide. Authors and activists were attracted to these tropes and texts not merely because they appeared to reveal concrete truths about long-hidden elements of American political life, but also because their very ambiguity enabled them to be flexibly co-opted. Conspiracy theories allowed activists to mobilize around shared gaps in public knowledge about traumatic events like the assassination, activating public dissatisfaction with official explanations of those events. Their ambiguity, coupled with the seeming pervasiveness of conspiracy theorist tropes across political divides, appeared to activists seeking realignment of both the left and the right as a promising tactical opportunity to assert that they and their erstwhile enemies were actually engaged in a shared project. Activists thus came to see conspiracy theory not as the province of an exclusively left or right politics, but as an autonomous and contestable cultural space. This, in turn, led to cross-partisan encounters. (shrink)