The stability of in-party voting suggests that either the parties are getting better at nominating high-quality candidates or membership in the parties has become more homogeneous — so that a typical candidate now gets the support of more partisans because partisans are now more alike than they were 50 years ago. There’s some evidence that both of these things are true, but another way to see the power of partisanship as a social identity is to look at something completely different: marriage.
People who identified with a party had even more intense feelings. In 1958, 33 percent of Democrats wanted their daughters to marry a Democrat, and 25 percent of Republicans wanted their daughters to marry a Republican. But by 2016, 60 percent of Democrats and 63 percent of Republicans felt that way.
People in each party now share more similar views on issues and they are more alike in race and ethnicity. Americans are increasingly surrounded by those who are like-minded — and they seem to prefer to keep it that way for the next generation.
