Donald Trump changed the GOP. But has he weakened it?

Most voters who were Republicans—or Democrats—in 2016 have stuck with their party

One of the more famous studies in political psychology found that people will defer to their party when deciding which policy positions they do or do not support. In his aptly-titled 2003 paper “Party Over Policy,” Geoffrey Cohen writes:

Four studies demonstrated the impact of group influence on attitude change. If information about the position of their party was absent, liberal and conservative undergraduates based their attitude on the objective content of the policy and its merit in light of long-held ideological beliefs. If information about the position of their party was available, however, participants assumed that position as their own regardless of the content of the policy. The effect of group information was evident not only on attitude, but on behavior (Study 4). It was as apparent among participants who were knowledgeable about welfare as it was among participants who were not (Study 2). Important alternative explanations for the obtained results, such as effects of heuri…