The prospect that the defeated Southern states might actually be able to control both the House of Representatives and the Electoral College so alarmed Republicans that they included a clause in the new 14th Amendment to prevent it. Because Southern states were denying voting rights to freed slaves, the clause reduced the population base used to allot House seats, based on how many adult male citizens in a state had been denied the right to vote.

Implementing that clause required adding a question about the citizenship status of adult males to the 1870 census, as well as a question about whether those citizens had been denied voting rights. But by the time the census took place, the 15th Amendment, which guaranteed voting rights to African-Americans, made the provision moot — and as the census soon showed, a population surge in the American West offset the South’s gains anyway.

The next time citizenship was on the form, in a question about naturalization in the 1890 census, it came with the rise of a virulent campaign against immigrants. Curiously, one of the campaign’s principal leaders was the superintendent of the 1870 and 1880 censuses, Gen. Francis Amasa Walker.

General Walker, who was also president of the Massachusetts Institute of Technology, became increasingly obsessed with what he saw as the pollution of the American genetic strain by inferior immigrants.

Seeking to pin down the nation’s lineage, he adjusted the 1880 census to inquire about not only the respondents’ birthplaces, but their parents’ as well. Later, he backed an 1882 law that banned Chinese immigrant labor, and he called immigrants from Italy, Hungary, Austria and Russia “beaten men from beaten races, representing the worst failures in our struggle for existence,” according to the book “Impossible Subjects: Illegal Aliens and the Making of Modern America,” by Mae M. Ngai.

When the 1890 census showed that immigrants had accounted for 40 percent of the nation’s population growth in the previous decade, General Walker assailed the head count as inaccurate, kicking off a Democratic-led assault on the census that killed legislation to set up a permanent census office.

The anti-immigrant furor had yet to subside by 1920, when census-takers asked about respondents’ birthplaces, immigration history and naturalization status, and also their parents’ birthplaces and mother tongues.