The startling 2016 presidential election weakened the notion of tribal identity rather than a shared American identity. And it may have begun a return to the old idea of unhyphenated Americans. Many working-class voters left the Democratic Party and voted for a billionaire reality-TV star in 2016 because he promised jobs and economic growth first, a new sense of united Americanism second, and an end to politically correct ethnic tribalism third. In the 19th century, huge influxes of Irish and German immigrants warred for influence and power against the existing American coastal establishment that traced its ancestry to England. Despite...