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In brief, inequality and party differences were substantial in the 1930s and 1940s. From the 1950s through the 1970s, both inequality and party divisions were declining. Since then inequality has increased, as have party differences about public policy (McCarty, Poole, and Rosenthal 2006). These long-term changes should have produced corresponding changes in class divisions (Stonecash 2006).
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Given these variations, the other important matter is whether the parties differ substantially on policy alternatives and whether voters recognize such differences. Previous research shows that differences between the parties follow a pattern very similar to that of inequality (Stonecash, Brewer, and Mariani 2003). Figure 2 presents party differences using the DW-NOMINATE scores developed by Keith Poole. Differences were relatively great during the first half of the 20th century and then gradually declined from the 1940s through most of the 1970s. Then the differences began to increase, and they are now as great as they were a hundred years ago (Gerring 1998, 125–158, 232–253; Stonecash 2006; Taylor 1996). Voters have recognized these growing differences. As Figure 3 indicates, respondents in national surveys increasingly say they see differences between the two parties and care about who wins the presidential election.