After pushing Homeland Security Secretary Kirstjen Nielsen out Sunday night, President Trump revived his threat to "close" the U.S.-Mexico border "and/or institute tariffs" to punish Mexico for Central American migration, adding: "Our Country is FULL!" That's hard to fact-check, since America doesn't have a fire marshal or a defined capacity, but a report released last week suggests that, in fact, much of America — especially America's rural "heartland" — is increasingly, troublingly empty.

The report, from Washington think tank the Economic Innovation Group, found that 80 percent of U.S. counties lost prime working-age adults (25-54) between 2007 and 2017, and 65 percent of counties will lose more prime workers in the next decade. Forty-one percent of U.S. counties, home to 38 million people, are "experiencing rates of demographic decline similar to Japan's," the report found. And "the demographic challenges facing large parts of the country are not benign," the authors add. "Demographic decline and population loss are not just symptoms of place-based economic decline, they are direct causes of it."

For example, "a shrinking supply of working-age people can prompt employers to look elsewhere to expand, making it harder for local governments to raise enough taxes to pay for infrastructure and education, and encouraging those younger people who remain to head elsewhere for more opportunity," New York Times economics correspondent Neil Irwin explains. These "left-behind" communities "can get stuck in a vicious cycle," potentially hitting "a point of no return that undermines the long-term economic potential of huge swaths of the United States."

The EIG, funded largely by tech investors and entrepreneurs, suggests creating a new kind of "heartland visa" for skilled immigrants willing to settle down and help revitalize struggling communities that agree to welcome them. But "regardless of what one thinks about using immigration policy to try to arrest demographic decline," Irwin writes, "demography may be the most powerful economic force of them all, and for much of the United States, the trend lines, for now, are pointing in the wrong direction." That direction is not toward "FULL!" Peter Weber