In the penultimate chapter of Why We’re Polarized, Ezra Klein argues that while the forces of polarization act on both major U.S. political parties, the Democratic party has managed to weather them whereas the Republican party has largely succumbed. That is, Republicans stand out for their growing violation of and downright hostility toward established norms. He multiplies examples to make the case at pp 228-9.
What accounts for the difference? Klein’s answer is that the forces of ideological sorting have made the Democratic party more internally diverse and the Republican party more internally homogenous: “Republicans are overwhelmingly dependent on white voters. Democrats are a coalition of liberal whites, African Americans, Hispanics, and Asians. Republicans are overwhelmingly dependent on Christians. Democrats are a coalition of liberal and nonwhite Christians, Jews, Muslims, New Agers, atheists, Buddhists, and so on. On the fixed versus fluid psychological dimensions…Republicans are overwhelmingly the party of fixed voters. But…Democrats are psychologically sorted only among white voters,” while psychological orientation aligns less with party affiliation among voters of color (230-1).
The upshot is that “Democrats need to go broad in order to win over their party and…they need to reach into right-leaning territory to win power. Republicans can afford to go deep” (231). And that means that Republicans can appeal to voters through appeals to group identity, whereas Democrats must use party platform and policy goals to unify a diverse collection of interest groups.