Partisan sorting
Partisan sorting is an effect in politics in which voters sort themselves into parties that match their ideology. Partisan sorting is distinct from political polarization, which is where partisans subscribe to increasingly extreme positions. As political scientist Nolan McCarty explains, "party sorting can account for the increased differences across partisans even if the distribution of...attitudes in the population remains unchanged or moves uniformly in one direction or the other." As an example given by McCarty, the gap between the Democratic Party and Republican Party on views towards immigrants strengthening the country with hard work and talents has widened from a 2-point gap in 1994 to a 42-point gap in 2017. A reasonable explanation is that of partisan sorting: those who are pro-immigrant shifted into the Democratic party and immigration-restrictions have shifted towards the Republican party.