For decades, Americans’ trust in one another has been on the decline, according to the most recent General Social Survey. A major factor in that downshift has been the concurrent rise in the polarization between the two major political parties. Supporters of Republicans and Democrats are far more likely than in the past to view the opposite side with distrust. That political polarization is so stark that many Americans are now unlikely to have friendly social interactions, live nearby or congregate with people from opposing camps, according to one recent study. Social scientists often refer to this sort of animosity...