Title: The Mechanisms of Elite Political Polarization in America
Description: The ideological divide in contemporary American politics is at a historic high. In this regard, many social scientists have documented the recent trends of political polarization in American politics and found robust evidence that political polarization has far-reaching consequences. While this kind of work is immensely important and revealing, significant lacunae still remain in our understanding of where political polarization comes from and how it could be lessened with what mechanisms. Prior studies of political polarization also have been largely concerned with numerically measuring ideology and polarization using voting records or survey instruments, but how deeply this polarization has filtered into political discourse with what kind of historically specific textual structure is less well known as well. In this dissertation, I bring the theory of cognitive schema and other micro-and-macro sociological accounts as sensitizing guides, and the tools of the natural language processing models to identify the mechanisms and origins of political polarization in America.

I leverage the newly digitized Congressional Record for exploring the modern political landscapes and discourse emergence dynamics and examining policy implications for how our results relate to broader pragmatic issues concerning interpersonal conflict and opinion compromise. In addition, I also aim to contribute to the sociological literature on shared cognitive schema, co-evolutionary dynamics of languages and structures, and political agency, respectively. Based on the textual details traced in raw congressional speech records along with the deep-learning-based word embeddings models of language, I extract the pairwise similarity of relational schematic configurations among the U.S. Senators from the texts and propose that the dyadic schematic similarity has direct positive consequences on ideological convergence. I also aim to shed new light on the co-constitutive nature of social ties and political languages and argue that interaction patterns within and across political parties are contingent on the structure of the social ties and on the language patterns that a pair of legislators have produced over time.

Finally, through a short case study, I develop measures of political agency in conversational texts. To our knowledge, this is one of the first comprehensive sociological studies that examines relational and discursive dynamics from the crucial modern moments of American politics. Because expressing conflict and making coordination in political domains are present in virtually all human contexts and constitute one of the fundamental bases of macro-level phenomena, a close understanding of the mechanisms behind intensified partisanship will also help policymakers understand the ramifications that merely micro-level political actions have on our social life during the very periods of "polarized America.".