  Social sorting, the alignment of social identities, affiliations, and/or
preferences with partisan groups, can increase in-party attachment and decrease
out-party tolerance. We propose that self-presentation afforded by social media
profiles fosters subjective social sorting by shaping perceptions of alignments
between non-political and political identifiers. Unlike previous work, we
evaluate social sorting of naturally occurring, public-facing identifiers in
social media profiles selected using a bottom-up approach. Using a sample of 50
million X users collected five times between 2016 and 2018, we identify users
who define themselves politically and generate networks representing
simultaneous co-occurrence of identifiers in profiles. We then systematically
measure the alignment of non-political identifiers along political dimensions,
revealing alignments that reinforce existing associations, reveal unexpected
relationships, and reflect online and offline events. We find that while most
identifiers bridge political divides, social sorting of identifiers along
political lines is occurring to some degree in X profiles. Our results have
implications for understanding the role of social media in facilitating (the
perception of) polarization and polarization mitigation strategies such as
bridging interventions and algorithms.
