This study focuses on the complex relationship between religious rhetoric and political discourse in the United States and presents an extensive analysis that spans from historical contexts to contemporary dynamics. Introducing a novel quantitative measure, the Religious Keyword Index (RKI), this research systematically quantifies the presence and evolution of religious language and conservative tone across state and national party platforms, presidential speeches, and, for comparative insight at the presidential level, the political discourse of Turkiye, a leading democracy within the Muslim world. The analysis reveals the deep historical roots and evolving application of religious rhetoric in American politics. Findings indicate a significant and stable divergence in the use of religious language between the Democratic and Republican parties, contributing to the polarized landscape of contemporary American politics, particularly noticeable from the early 2000s onwards. Beginning with the Gulf War and 9/11, this era marks a pivotal shift: the Republican Party seemed to be increasingly incorporating religious rhetoric into its political messaging, potentially aligning with its discernible orientation towards social conservatism and evangelical voter bases. A thematic examination of RKI metrics across various political and social issues uncovers the selective application of religious rhetoric and particularly highlights its potent role in discussions around social and family values. This theme-based analysis potentially offers insights into the specific areas in which parties deploy religious language to resonate with targeted constituencies. Moreover, the study extends its analysis to the international arena by comparing the RKI of American political discourse with that of Turkiye at the presidential level, which underlines the broader global implications and the diverse roles religious rhetoric plays in different democratic contexts. This comparative perspective situates the American experience within a wider global framework. Conclusively, this research enriches the scholarly discourse on the intersection of religion and politics by offering a comprehensive qualitative and quantitative analysis of religious rhetoric in American political communication within an evolving political and global landscape. As the use of religious language becomes more pronounced, understanding its implications for political cohesion, public discourse, and democratic engagement is increasingly imperative.