An overlooked topic of the Hart-Fuller debate is Lon Fuller’s critique of HLA Hart’s rule of recognition. The core of Fuller’s critique is that Hart’s approach is “legalistic”. The aim of this paper is to revisit this critique, explain what Fuller understands by “legalism”, and argue that his claim has the potential of illuminating current discussions on a relevant dimension of judicialization of politics. Judicialization of politics involves both (i) the transfer of authoritative decisions of fundamental political questions and issues of public policy from the legislative to the judicial forum, as well as (ii) what some have called “the juridification of social life”. My claim is that this latter dimension is an instance of “legalism”. If so, and if judicialization of politics presents a challenge to contemporary constitutionalism, as some have argued, examining Fuller’s account will provide a fresh perspective to analyze the range and scope of that challenge.