Immigrants from Central America await transport from the U.S. Border Patrol in Roma, Tex., last month. (John Moore/Getty Images)

The conversation — or argument — we’ve been having on immigration has been remarkably skewed. It’s been all about the estimated 11 million illegal immigrants, otherwise known as the “undocumented.” Actually, what counts far more are the estimated 31 million immigrants who are here legally and the roughly 1 million who gain legal entry every year.

Of course, the question of undocumented immigrants is important. As a society, it’s intolerable to have so many people living in a legal twilight zone, often despite years of responsible and law-abiding behavior (two-thirds of illegal immigrants have been in the United States for 10 years or more, reports the Pew Research Center). Still, one powerful reason for settling this issue — to legalize most of those already here and to suppress new illegal flows, even with a wall — is to move on to larger subjects.

We need an immigration system that gives priority to skilled over unskilled workers, rather than today’s policy that favors family preferences for green cards. This sort of system would promote assimilation (because skilled workers have an easier time integrating into the workforce and society), increase economic growth (because skilled workers have higher “value added” than unskilled labor) and reduce poverty (because many unskilled immigrants have incomes below the government’s poverty line).

Although we can’t easily quantify these benefits, they would promote the greater good for an aging society with a sputtering economy. Anyone who doubts immigration’s pervasive influence should examine a massive report issued last week by the National Academies of Sciences, Engineering, and Medicine. It’s titled “The Economic and Fiscal Consequences of Immigration.” Here are some highlights.

● Immigration is no longer a side issue. From 1995 to 2014, the number of immigrants increased from 24.5 million (9 percent of the population) to 42.3 million (13 percent). When the children of immigrants are added to the total, nearly 1 in 4 Americans is of immigrant stock. Immigrants are increasingly shifting from traditional “gateway” states (California, New York, Florida) into nontraditional states (North Carolina, Georgia, Tennessee and Nevada).

● The number of illegal immigrants has stabilized at about 11 million since 2009. The number of Mexicans illegally in the United States declined from 6.4 million in 2009 to 5.8 million in 2014. Others have taken their place. All these figures represent “net changes” — illegal immigrants entering the United States minus those leaving. Although these flows now roughly balance, they’re still huge, averaging about 300,000 to 400,000 annually.

● Poor immigrants — heavily from Latin America — have increased U.S. poverty. In 2011, the poverty rate (the share of the people below the government’s poverty line) was 35 percent for Mexican immigrants and their children and 22 percent for El Salvadoran immigrants; by contrast, the poverty rate was 11.1 percent for Korean immigrants and their children and 6.2 percent for Indian immigrants. The poverty rate for all native-born Americans was 13.5 percent.

● Immigrants and their children impose costs on government, mainly for local schooling, which the Supreme Court has decreed must be provided for all immigrant children. By contrast, Congress has barred even legal immigrants from receiving some federal benefits. In 2013, the study estimated, immigrants’ costs to government exceeded their taxes by $388 billion, slightly more than 2 percent of gross domestic product.

What justifies immigration if it generates more in government costs than in taxes? The answer is that the benefits of immigration can — and, in this case, do — go beyond taxes. By one estimate, immigrants (including their entrepreneurial activity) have increased the size of the U.S. economy by 11 percent or about $2 trillion. With baby boomers retiring, all the projected growth in the U.S. labor force from 2020 to 2030 stems from immigrants and their children, the study reported.

The gains from immigration would be magnified if we emphasize high-skilled workers. Productivity would be higher, poverty lower. Interestingly, this also would help low-skilled Americans, both natives and recent immigrants. They wouldn’t have to compete against new low-skilled immigrants, who would vie for their jobs and depress wages.

Whether we have the political competence and courage to face these issues candidly is an open question. The study deliberately steered away from policy prescriptions; it was mainly a fact-finding exercise, reflecting (presumably) the subject’s controversial nature.

The presidential campaign offers little ground for optimism. Donald Trump has used immigration as a wedge issue and shows little understanding of the underlying substance. Hillary Clinton seems intent on placating her Hispanic supporters, many of whom surely support family preferences for immigrating legally to the United States.

Republican presidential nominee Donald Trump described his proposed wall along the Southern U.S. border during an immigration policy speech Wednesday. (Victoria Walker/The Washington Post)

But the underlying realities will not retreat no matter how much we wish they would. If we cannot maneuver immigration to our advantage, it will almost certainly work to our disadvantage.

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