A political realignment is a set of sharp changes in party-related ideology, issues, leaders, regional bases, demographic bases, and/or the structure of powers within a government. In the fields of political science and political history, this is often referred to as a critical election, critical realignment, or realigning election. These changes result in a restructuring of political focus and power that lasts for decades, usually replacing an older dominant coalition. Scholars frequently invoke the concept in American elections as this is where it is most common, though the experience also does occur in governments across the globe. It is generally accepted that the United States has had five distinct party systems, each featuring two major parties attracting a consistent political coalition and following a consistent party ideology, separated by four realignments. Two of the most apparent examples include the 1896 United States presidential election, when the issues of the American Civil War political system were replaced with those of the Populist and Progressive Era, and the 1932 United States presidential election, when the issues of the Populist and Progressive Eras were replaced by New Deal liberalism and modern conservatism. Realigning elections also contribute significantly to realigning (what are known in the field of comparative politics as) party systems—with 1828, for example, separating the First Party System and the Second Party System in the US.
Political realignments can be sudden (1–4 years) or can take place more gradually (5–20 years). Most often, as demonstrated in V. O. Key Jr.'s (1955) original hypothesis, a single "critical election" marks a sudden realignment. However he also argued that a cyclical process of realignment exists, wherein political views within interests groups gradually begin to separate which he designated as secular realignment. Political scientists and historians often disagree about which elections are realignments and what defines a realignment, and even whether realignments occur. The terms themselves are somewhat arbitrary, however, and usage among political scientists and historians does vary. In the US, Walter Dean Burnham argued for a 30–38 year "cycle" of realignments. Many of the elections often included in the Burnham 38-year cycle are considered "realigning" for different reasons.
