  The causes for the rise in affective polarization are debated, primarily
revolving around ideological polarization and partisan sorting hypotheses. The
former indicates divergent ideological beliefs on key issues as the main fuel
for the increasing political divide. The latter, instead, proposes that the
alignment of social identity with partisan affiliation intensifies partisan
rift. We present a novel methodology using data from the American National
Election Studies (ANES) to discern the contributions of both ideological
polarization and partisan sorting to affective polarization. We quantify
multidimensional polarization by embedding ANES respondents to a variety of
political, social, and economic topics into a two-dimensional ideological
space. We identify several demographic attributes (Race, Gender, Age,
Affluence, and Education) of the ANES respondents to measure their alignment
with partisan affiliation. Our results show that income and especially racial
groups are strongly sorted into parties, while education is orthogonal to
partisanship. By analyzing the trajectories of political and demographic groups
across time, we observe an increasing partisan divide, due to both parties
moving away from the center at different rates. Opinions within groups become
increasingly heterogeneous in the last decade, with a share of Democratic
voters moving to a novel region of the ideological space. We conclude that the
observed growth in partisan divide is due to a combination of partisan sorting
and increasing ideological polarization, mainly occurring after 2010.
