Party polarization in American politics: Characteristics, causes, and consequences

Recent commentary points to clear increases in ideological polarization between the major American political parties. We review the theoretical and empirical literature on party polarization and partisan change. We begin by comparing the current period both to earlier political eras and to theories of partisan change. We argue that in the current period the parties have grown increasingly divided on all the major policy dimensions in American politics-a process that we term conflict extension. We discuss various perspectives on increases in polarization between the parties in government, the parties in the electorate, and the parties' activists, and we consider the causal links between polarization at each of these levels. We consider whether American society itself, and not just the parties and their identifiers, has become increasingly polarized. Finally, we discuss the consequences of growing party polarization for American political life.