Parties used to be based on precincts, which covered broad swaths of people, albeit often people with similar profile. That changed as data allowed politicians to focus on individual voters rather than communities. See From Precinct to Voter
What has been the result? Perhaps it is data which is to blame for the “rise of lifestyle politics”. Consider the political change that David Frum describes:
Politics was becoming more central to Americans’ identities in the 21st century than it ever was in the 20th. Would you be upset if your child married a supporter of a different party from your own? In 1960, only 5 percent of Americans said yes. In 2010, a third of Democrats and half of Republicans did. Political identity has become so central because it has come to overlap with so many other aspects of identity: race, religion, lifestyle. In 1960, I wouldn’t have learned much about your politics if you told me that you hunted. Today, that hobby strongly suggests Republican loyalty. Unmarried? In 1960, that indicated little. Today, it predicts that you’re a Democrat, especially if you’re also a woman.
This is just a thought, but how much of this is the result of data which allows us to cobble together party support based on individual demographic data, and target people within communities via phone and email and personalized web ads? The political class’s fascination with Soccer Moms and NASCAR Dads and the like inspires some eye-rolling, but these are demographic communities that would not even be targetable in 1960 by traditional GOTV efforts.
There’s a link here to this idea of Imagined Communities though I haven’t hashed this out.
Part of the reason for the marriage statistic is simply that the parties were not seen as that far apart on anything, at least by some. See Dime-Store New Deal