When the Census Bureau asks Americans about their ancestors, some respondents don’t give a standard answer like “English” or “German.” Instead, they simply answer “American.”

The places with high concentrations of these self-described Americans turn out to be the places Donald Trump’s presidential campaign has performed the strongest.

...

Mr. Trump has his share of support from the affluent and the well educated, but in the places where support for Mr. Trump runs the strongest, the proportion of the white population that didn’t finish high school is relatively high. So is the proportion of working-age adults who neither have a job nor are looking for one. The third-strongest correlation among hundreds of variables tested: the preponderance of mobile homes.