Party Identification
Party identification is an important attitude that influences the vote (Campbell et al. 1960; Lewis-Beck et al. 2008; Green, Palmquist, and Schickler 2002). Most voters identify with one of the two major political parties, and these basic partisan loyalties influence their behavior. Party identification normally is measured by asking individuals whether they consider themselves to be a Democrat, Republican, or independent. Those indicating Democratic or Republican are then asked whether they are a strong or a weak Democrat or Republican, while those claiming to be an independent are asked whether they feel closer to one of the two political parties. This yields a sevenfold classification: strong Democrats, weak Democrats, independents closer to the Democrats, independents not closer to either party, independents closer to the Republicans, weak Republicans, and strong Republicans. This seven-point party identification scale is in the dataset.
The influence of party identification on the vote is strong. However, not many voters in 2016 cast a ballot for Donald Trump simply because he was a Republican or for Hillary Clinton only because she was a Democrat. Rather, partisan loyalties influence evaluations of candidates, assessments of government performance, and perceptions of political events. Put simply, party identification is a perceptual screen—a pair of partisan-tinted eyeglasses through which the voter views the political world. Thus, most Republicans developed many reasons to vote for Trump, and most Democrats many reasons to prefer Clinton.
Moreover, partisan hostility has grown substantially over the past two or three decades. Increasingly, Democratic voters have very negative views of Republicans, and Republican voters have extremely unfavorable perceptions of Democrats (Abramowitz 2014; Kimball, Summary, and Vorst 2014). With each group of partisans so hostile toward the other side, it becomes more difficult to persuade voters to cast a ballot for the candidate of the other party. Independents are a more persuadable group, but pure independents—i.e., those who do not lean toward a party—are only a small share of the electorate. Most independents lean toward one of the two parties, and these independent leaners are more similar to the partisan identifiers than they are to the pure independents.