But we, the electorate, have surely helped Trump with what's most often called (with a lack of political correctness) our tribalism. As the author of a new book called Uncivil Agreement: How Politics Became Our Identity, University of Maryland political scientist Lilliana Mason, spells out, "our conflicts are largely over who we think we are rather than over reasoned differences of opinion." In other words, the sorting of the parties that took place after the civil rights battles of the 1960s — as the GOP became uniformly conservative and Democrats became solidly liberal — meant that party ID, and deep distrust of the other party, became core to our overall identity. That deep psychology is what Trump is tapping into when he blames Democrats for the caravan, however irrationally.