“Our argument centers on three elements. First, long-term tectonic shifts have pushed the parties apart while making the views within each party more uniform. This is the familiar trend toward gradually increasing partisan polarization. Second, shorter-term shocks, catalyzed especially by Trump, have sped up polarization on identity issues-those related to race, ethnicity, religion, and gender, And third, it is precisely these identity issues that voters in both parties care more about-exacerbating divisions even further and giving politicians every incentive to continue to play to them.”