Throughout the 20th century, Illinois supported winning candidates in twenty-three out of twenty-five presidential elections. However, in the 21st century, Illinois supported winning candidates in two out of five presidential elections. The state’s divergence from national trends followed three partisan shifts that occurred in the mid-to-late 20th and early-21st centuries. These shifts altered the state’s partisan preferences. While the causes of each shift varies, Illinois’s changing demographics, the concentration of its population in the Chicago Metropolitan area, and the rise of the post-industrial economy, caused the state to depart national trends as Illinois increasingly supported Democrats.

The presidential contest of 1952 established a new trajectory for Florida politics. This pivotal election reversed decades of Democratic dominance and signified the beginning of presidential Republicanism in the state. Elections in the second half of the 20th century provided evidence of an increasingly favorable environment for Republican nominees. During this period Democrats were limited to carrying the state's electoral votes three times. GOP presidential ascendancy in Florida was augmented by partisan conversion and the disproportionate in-migration of white Northerners following World War II. Contrary to unrivaled 1980s support, which created an anchor in a new core Southern Republican electoral bloc, the 1990s restoration of competitiveness highlighted voter fluidity. This trend was exemplified by a virtual tie in the 2000 election. This paper confirms an atypical regional diffusion of Republican presidential dominance attributable to demographics. Contemporary Florida elections have been profoundly altered by an older population, increasing diversity due to immigration, and the erosion of Southern culture. Unlike intensifying national sectionalism, Florida has been classified as a "too close to call" during most of the past four presidential campaigns. A unique partisan balance is a component of a demographic profile mirroring the nation. Steady population growth has gradually positioned Florida as an unexpected presidential bellwether. The longevity of highly competitive national elections will continue to be primarily dependent on the partisan inclinations of newcomers.

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