This chapter offers an insight on the intellectual relationship between Reinhold Niebuhr and John Courtney Murray, SJ. Newly discovered archival documents highlight their roles as consultants to the Basic Issues Program of the Center for the Study of Democratic Institutions (CSDI), established in 1957. The activities of the programme were based on debates pertaining to topics including religious pluralism, civic unity, and natural law. Niebuhr and Murray had the opportunity to present their perspectives on the United States religious landscape and the issues raised by ecumenical and social relations between the Protestant majority and the Catholic minority. What emerges from their confrontation is not a search for conciliation, but rather a representation of Reinhold Niebuhr’s understanding of pre-conciliar Catholic theology and John Courtney Murray’s effort to contribute to the acknowledgement of Catholics within American history and society.