Updated at 1:14 p.m. ET

Like many of President Trump’s policies, the White House’s recent embrace of a plan to cut legal immigration in half rests on a fundamental misunderstanding of the economic relationship between “the brown and the gray.”

That’s the phrase I’ve applied to America’s increasingly diverse younger generations and its predominantly white older population. Today, kids of color represent nearly half of Americans 19 years old and younger and exactly half of the under-10 population. As Brookings Institution demographer William Frey recently calculated from Census data, the absolute number of white kids under 15 (not just the share) declined in 41 of the 50 states from 2010 to 2016—while the number of minority kids increased in 46 states.

Whites, meanwhile, compose almost four-fifths of all Americans age 65 and older and over two-thirds of the population age 45 to 64. Put another way, while nearly half of all whites today are 45 or older, nearly half of all non-whites are 30 or younger.

On many fronts, Trump effectively treats these two groups as competitors in a zero-sum struggle—and then looks to advantage the gray. That instinct is evident, for instance, in the president’s determination to slash spending on federal programs that invest in the productivity of (heavily diverse) future generations, such as education and scientific research, while cutting taxes for the (mostly white) families in the top income brackets and protecting entitlements for the (mostly white) elderly. It resurfaces in the Justice Department’s opposition to affirmative-action programs in higher education. And it pulses through his push to tightly squeeze the future flow of legal immigrants.

On these fronts and others, Trump’s policies fail to recognize the interdependence of the brown and gray. Rather than fundamentally competing with younger America, older America needs it to succeed.

With the number of young whites shrinking, the kaleidoscopically diverse Millennials and post-Millennials—as well as the potential legal immigrants who might join them—constitute much of the nation’s future workers, consumers, and taxpayers. The country’s mostly white older population needs a growing workforce that propels more young people into the middle class to generate the payroll taxes that sustain Social Security and Medicare. Though political divides obscure the link, there is no financial security for the gray without economic opportunity for the brown.

The immigration debate captures this dynamic. At his contentious press briefing last week, White House senior policy adviser Stephen Miller sold Trump’s endorsement of legislation from Republican Senators Tom Cotton of Arkansas and David Perdue of Georgia to cut legal immigration in half and favor higher-skilled workers as a way to protect the economic interests of lower-skilled, native-born workers.

But the most thorough economic research has concluded that immigration poses a very limited threat to those Americans. As I wrote earlier this year, the National Academy of Sciences, in an exhaustive study last fall, found “little evidence” that increased immigration significantly affected employment levels for native-born workers. The academy did find indications that immigration has pressured wages for lower-skilled workers, but even those effects were “very small … when measured over a period of 10 years or more.” They were also confined largely to recent immigrants and native-born workers who didn’t finish high school, groups that constitute a small share of the overall workforce.

Choking off immigration as severely as Cotton, Perdue, and Trump are proposing would impose other costs. Fewer new workers would mean slower overall economic growth. (In a report released Thursday morning, the National Immigration Forum quotes one economic forecast that projects cutting legal immigration in half would reduce annual economic growth by about one-eighth.) Business start-ups would be pinched, too, since immigrants start new companies at rates exceeding their share of the population. And a big slowdown in immigration would threaten the nation’s retirement safety net.

The Social Security trustees estimate the number of seniors will grow from 48 million now to 86 million in 2050. Under the current immigration laws, the Pew Research Center projects the working-age population will increase through 2065 by nearly as much, about 30 million. Pew estimates that immigrants, who tend to be younger, and their descendants will provide the vast majority of that increase. But if legal immigration is halved, Pew projects virtually no growth in the workforce.

That means roughly the same number of workers would need to support nearly 80 percent more seniors. That’s a recipe either for unsustainable tax increases or big benefit cuts in the Social Security and Medicare programs indispensable to Trump’s base.

“Trump’s immigration plan may seem to be a politically expedient way to reach older whites who are fearful of the nation’s changing demography,” Frey told me. “But … as more white baby boomers retire, the nation’s labor force and economic vitality will increasingly depend on [growingly] non-white immigrants and their children. They will be prime contributors to Social Security and Medicare.”

A preview of this dynamic is already evident in the Rustbelt states that keyed Trump’s win. As the Chicago Council on Global Affairs recently reported, the native-born, prime-working-age population declined from 2000 to 2015 in all but one of the 46 major Midwest metro areas. But 39 of those communities partially offset the loss by adding immigrants in that productive group, who are ages 35 to 44. Global Detroit and the Michigan Economic Center, two research and advocacy groups, could have been describing the entire region when they concluded in a recent study that “in Michigan … immigrants have been the main source of population gains and economic revival for once thriving industrial communities experiencing many years of decline.”

Like the attempt to repeal the Affordable Care Act, or the coming drive to slash food stamps, a massive cut in legal immigration would satisfy the ideological impulses of many in Trump’s older and blue-collar white base—while threatening their economic interests.