Between 1909 and 1941, the Russell Sage Foundation (RSF) was actively involved in crafting and lobbying for policy solutions to the pervasive problem of predatory lending. Using a rich assortment of archival records, I build upon political learning theory by demonstrating how institutional conditions and political pressures – in addition to new knowledge gained through scientific study and practical experience – all contributed to the emergence and development of RSF experts’ policy ideas over the course of this 30-year period. In light of these findings, I suggest that policy ideas and political interests are mutually constitutive, and that the notion that ideas must be shown to operate independent of interests in order to “prove” that they matter in policymaking is misguided. Furthermore, I discuss the implications of the remarkable success of RSF’s policy proposals for current understandings of institutional change. In particular, I argue that the passage of RSF’s controversial Uniform Small Loan Law in 34 states suggests that political actors’ collective agency can produce significant policy reforms in a context of normal policymaking without the intervention of major destabilizing events.