Mass demographic changes in the ethnic and racial composition of the United States since the 1960s are commonly considered a force driving major transformations in contemporary American politics. In political science, there are longstanding research traditions that examine the political implications of demographic change: how demographic change leads to growing intergroup political contestation over political power and public policies; how demographic changes lead to shifts in the group bases of partisan support; how demographic changes are associated with changes in the demographic composition of politicians and elected officials; and how the changing face of America affects the political responsiveness of elected officials to historically underrepresented but increasingly prominent segments of the population. Despite the proliferation of empirical studies on these topics, numerous causal claims central to broader arguments about the political implications of demographic change deserve greater theoretical and empirical scrutiny. In this dissertation, I make use of novel datasets and methods for descriptive and causal inference to contribute more credible evidence that test these claims and develop new avenues of research.