President Trump speaks during a news conference at the White House on March 6. (Jabin Botsford/The Washington Post)

PRESIDENT TRUMP makes no secret of his distaste for immigrants, nor of his support for measures to slash both legal and illegal immigration. Even as his crusade to close borders intensifies, however, American employers in an array of industries — manufacturing, agriculture, trucking, home building, energy, food service, retail and others — are warning that a long-brewing labor shortage is reaching crisis proportions.

The causes of America’s worker shortfall include an aging population and a birthrate that recently hit a historic low. With the jobless rate bumping along at just above 4 percent, companies desperate to fill orders and meet demand are pumping up their recruiting budgets and in some cases turning to ex-convicts to fill jobs.

If the employee deficit seems bad now, signs indicate it will get worse — even as Mr. Trump orders stepped-up deportation efforts and pushes legislation to slash annual legal immigration, currently about 1 million, by half. In a Barron’s article titled “The Great Labor Crunch,” a Wall Street strategist, Thomas J. Lee, projects a nationwide shortage of 8.2 million workers in the coming decade.

The Wall Street Journal reports that if every last jobless citizen in the 12 Midwestern states filled an open job in the region, 180,000 positions would still be left unfilled. Wisconsin is so starved of workers that it has launched a $1 million marketing campaign aimed at luring millennial job applicants from Chicago — where the jobless rate is just above 5 percent.

The argument that sufficient numbers of workers would materialize if employers raised wages is crumbling in the face of demographic reality. By 2030, the Census Bureau reports, the U.S. working-age population is projected to grow by 3 percent even as the total population balloons at three times that rate — an imbalance owing mainly to aging. Five years later, the number of Americans age 65 or older will outstrip those under 18 for the first time ever. Although more people are delaying retirement, economists say an aging population will depress productivity growth, which has already slowed alarmingly.

Columnist Eugene Robinson says President Trump's frenzied tweets about a "caravan" of migrants are really about his fear of losing his base. (Gillian Brockell/The Washington Post)

Mr. Trump says that the U.S. immigration system should tilt toward favoring more skilled and English-proficient workers; in fact, the legislation he backs would freeze the number of such immigrants at current levels while drastically reducing unskilled ones. The trouble is that employers in food processing, retail, landscaping and other industries that rely on low-skilled labor are already desperate for workers. If they can’t hire immigrants, who will fill those jobs? In Canada, which Mr. Trump extols for favoring more educated immigrants, companies report soaring worker shortages.

There’s a model for what Mr. Trump advocates — an unsuccessful one. It’s Japan, whose own fading economic prospects are a direct result of an aging population and an array of barriers to immigration.

Nativism has paid political dividends for Mr. Trump; it is highly unlikely to pay economic ones. By driving away legal and illegal immigrants even as unemployment flatlines and baby boomers retire, he deprives businesses of oxygen in the form of labor. That’s not a recipe for making America great.