Reddit mentions of Partisan Hearts and Minds

SK: Thanks for the question! Americans are deeply committed to their party identification and many equate party ID to a type of social identity. (Examples here and here just to name a couple of many.) As the question asker, states, social identity theory tells us that individuals view their in-group as a reflection of themselves and are thus motivated to evaluate their in-group positively and out-groups negatively. This in-group vs. out-group in politics can indeed lead Americans to unduly derogate the other party.

There are instances, though, where partisan adversaries can become less, for lack of a better word, adversarial. The Common In-Group Identity Model suggests that cueing a superordinate identity can unite rival groups. For example, Dr. Matthew Levendusky at the University of Pennsylvania finds that priming Democrats and Republicans to think of themselves all as Americans can unite the two groups. In ongoing research with Yanna Krupnikov and John Barry Ryan, I am finding that Americans are more tolerant of members of the opposing party when those individuals are not politically active. In other work I've done, I have found that bringing Democrats and Republicans together in face-to-face groups to allow for inter-personal discussion actually leads to more moderate and bipartisan policy preferences. So there are certainly moderating circumstance that can temper group rivalry between the two parties, at least within the mass public.

In political science most of the literature on vote choice, at least in contexts with stable party systems, builds out of the loyalties people have to political parties. Partisanship creates what the authors of the seminal work The American Voter call a "perceptual screen" which filters information in ways that reinforce these ties. In other words, people first identify with a political party, then interpret the world in ways that support these views (think confirmation bias and motivated reasoning). This identification, moreover, typically [comes from parents](http://press.princeton.edu/titles/654.html] or other early social experiences.

Vote choice and candidate preference then follows from these loyalties. Loyalties to a political party is symbolically and psychologically meaningfully, much like supporting a sports team or adhering to given religious tenets. That's why you'll see people sticking by candidates regardless of information, among many other political phenomena.

See this in the NYTimes for a quick overview.