Partisanship and Polarization

In the mid-twentieth century the two parties overlapped considerably, with conservative Southern Democrats and liberal Northeastern Republicans often voting across party lines. In 1950 a committee of the American Political Science Association actually urged the parties to become more distinct and disciplined. Measures of congressional voting developed by political scientists Keith Poole and Howard Rosenthal show that polarization began rising in the 1970s, and by the early 2000s the most conservative Democrat in Congress was typically more liberal than the most liberal Republican.

Scholars cite several causes: the realignment of the South from Democratic to Republican after the civil rights laws of the 1960s, the sorting of voters so that ideology and party line up more closely, the rise of partisan media and social media, primary elections dominated by committed voters, nationalized campaigns, and growing geographic separation between urban and rural voters. Researchers disagree about how much gerrymandering contributes, since the Senate, whose districts are fixed state lines, has polarized too. Many studies find polarization has been greater among Republicans in Congress, a finding others dispute.

Polarization now extends to how voters feel about the other party, a pattern called affective polarization, and surveys by the Pew Research Center and others show that large shares of each party view the other unfavorably and as a threat. Supporters of strong parties say clear differences give voters real choices and make parties accountable for their records. Critics say extreme polarization produces gridlock, weakens trust in elections and institutions, and makes compromise politically dangerous. Proposed responses include open or ranked-choice primaries, independent redistricting, and changes to campaign finance.