Beneath all of this is the bedrock problem of illegal immigration into an advanced society. In 1914, it was perfectly plausible that the son of an unskilled laborer would acquire a skilled trade. The skilled worker’s children would then advance into business and the professions, achieving the upward mobility of the American dream.

In the postindustrial economy, however, upward mobility has become considerably more difficult. As Edward Telles and Vilma Ortiz report in their pathbreaking Generations of Exclusion: Mexican Americans, Assimilation, and Race, the kind of intergenerational progress gained by millions of families in the early 20th century is receding out of reach for many newer immigrants. While second-generation Mexican Americans generally attain higher levels of schooling than their immigrant parents, the third generation does not on average improve much on the second—and the fourth generation on average falls back below the third.

From the point of view of immigrants and prospective immigrants, the only thing that matters about immigration policy is what it does for them and their own life chances. Human beings naturally put their own interests first. But from the point of view of the present generation of Americans, the most important question about immigration is whether immigration will benefit the present citizens of the United States, their children and posterity.