The Madisonian formulation suggests that (religious) pluralism is linked to moderate representation when filtered through republican selection. We leverage the quasi-experiment afforded by the ratification of the 17th Amendment to explore whether religious diversity shapes how senators vote. The shift from indirect to direct elections, coupled with roll-call and religious Census data, allows us to test hypotheses derived from differing conceptions of pluralism and the literature on constituency effects in Congress. We find that religious diversity is linked to ideological moderation, but that link weakens considerably in the immediate aftermath of the amendment’s passage.