The 1990s party realignment of U.S. presidential elections: Geographic sorting of counties by blue or red.

Introduction: This paper addresses the issue of partisan polarization in the U.S. in presidential voting at the county level. The literature on the growing partisan sorting and/or polarization is extensive, and controversies are pervasive. This paper focuses on the timing and sequence of changes in partisan vote shares at the county level from 1952 through the 2020 election. Methods: We apply confirmatory factor analysis to identify the structures of partisan competition in counties from 1952 to 2020, and multiscale geographically weighted regression (MGWR) to uncover the social processes that influence the growing partisan polarization in the U.S. Results: We find that the growing partisan segregation coincides with the beginning of a secular change in the structure of partisan competition at the presidential level among counties that has intensified over the past quarter century. Polarization, segregation of partisans in communities, and a rise in sectionalism are the predominant characteristics of this new alignment. Conclusion: This study confirms a secular realignment in the structure of party competition among counties in presidential elections starting in 1996 and solidifying in 2008 when Obama is elected. The segregation of counties by dark shades of red or blue is the unique fingerprint of this new alignment that we call the "Geographic Sort" alignment. [ABSTRACT FROM AUTHOR]