This article describes debates among members of the Frankfurt School during their years in exile in the United States about the status of political institutions within their analytic frameworks. The cited unpublished material in this article sheds new light on the complicated relationship between Otto Kirchheimer and the core of the Frankfurt School group on this issue. Kirchheimer’s biographical episode with the group exemplifies both the failure of interdisciplinary collaboration at the Institute of Social Research and the inability of its members to develop a joint theoretical perspective on political phenomena. In the context of the Frankfurt School, Kirchheimer’s works present a countermodel to the interpretation of modern mass democracy as an integrative regime of instrumental reason. He refused to accept such a global interpretation. In his work at the Institute of Social Research he accentuated the unequal power recourses of conflicting social groups and different institutional mechanisms to deal with these conflicts politically. This approach made his work interesting for authors of a later generation of Critical Theory like Jürgen Habermas and Claus Offe.