President Donald Trump’s renewed crusade against legal immigration poses a direct threat to the long-term financial interests of the older White Americans who remain his core supporters.

Since the tragic shooting of two National Guard troops in Washington, D.C., last week by a man from Afghanistan, Trump has directed a fusillade of invective not only at undocumented immigrants, refugees and foreigners seeking asylum, but at all of the nation’s foreign-born population —nearly 52 million people. He has pledged to retrench multiple avenues for legal immigration and to remove an untold number of immigrants already in the US through a process of “reverse migration” — a phrase associated with far-right European parties.

Trump’s call for such restrictions has a powerful appeal to his base voters’ cultural anxieties about a changing America. (Majorities of Republicans and Trump voters tell pollsters they believe the large number of immigrants admitted to the US in recent years threatens the nation’s traditional values and customs.) But seriously reducing, much less reversing, immigration to the US directly threatens the economic interests of those same voters.

If Trump succeeds in slashing legal immigration over the long term, he will virtually guarantee future cuts in Social Security and Medicare, the social safety net programs for the elderly that are funded by payroll taxes on workers.

Without immigration, Census data analyzed by demographer William Frey of the Brookings Metro think tank indicate that the working-age population (defined as adults between ages 18 and 64) will very quickly start to shrink — thus reducing the number of workers available to fund the programs. That’s an ominous prospect when the number of seniors is projected to rapidly increase and the programs already face looming financial strains.

Immigrants are indispensable to the stability of those social safety net programs because the growth of the native-born population has dramatically slowed. As recently as 2007, there were nearly 1.8 births for every death in America; in 2023, the latest year for which figures were available, the US saw only about 1.16 births for every death. (The ratio was even lower during the pandemic.) Non-Hispanic Whites have experienced more deaths than births since 2016.

Natural increase will still add to the country’s population for a while because Black, Asian-American, mixed-race and Hispanic Americans continue to experience more births than deaths. But the Census Bureau projects that by 2038, deaths will exceed births for the nation as a whole, and through the 2040s that deficit will reach 500,000 or more annually. Given those trends, immigration “basically determines whether the population will grow or not,” says Jeffrey Passel, a senior demographer at the nonpartisan Pew Research Center.

A declining population might not be so damaging, Frey points out, “If all the different age groups shrunk at the same rate.” The problem is that in a low-immigration future, the youth and working-age population would be shrinking as the final baby boomers and first members of Gen X age into retirement.

Using Census data, Frey has calculated that if all immigration were stopped, America’s working-age population would fall by about 5% through 2035; even under the reduced levels of immigration that the US experienced during Trump’s first term, the working-age population would fail to increase at all. Under either of those scenarios, Frey projects, the youth population (younger than 18) would decline even faster than the working-age cohort. Meanwhile, calculations Frey provided to me from the latest Census data show that the number of seniors will rise by about 20% just through 2035; over the next two decades, Frey forecasts that the number of seniors older than 80 — who generate much larger bills per person for Medicare than people in their 60s and 70s — will double.

More seniors and fewer workers are a recipe for cuts in Social Security and Medicare, since the shrinking number of future workers could not realistically bear the taxes that would be required to sustain benefits at current levels. Beyond the fiscal pressure on Social Security and Medicare, restricting immigration would also reduce the number of younger workers available to physically provide care for the expanding senior population (since immigrants account for nearly 3 in 10 home health care workers).

All of that would directly threaten the financial (not to mention the physical) wellbeing of Trump’s electoral base. For all of Trump’s success at diversifying his electoral coalition in 2024, exit polls suggest that White people aged 45 and older still provided nearly three-fifths of his votes, well above their share of all ballots. Older, blue-collar White voters are equally central to House Republicans — most of whom now represent primarily White, working-class districts where the median income lags the national average. No one in either party has tried on a sustained basis to explain how immigration restrictions would threaten Social Security and Medicare, but Trump is opening the GOP to those arguments at a time when the party is more reliant than ever on working-class voters who need the programs now or in the future.

Trump has long recognized that the working-class base he has built for the Republican Party prizes Social Security and Medicare and has, since his first campaign in 2016, steered the GOP away from its earlier attempts to directly retrench those programs. But his attempts to curtail legal immigration will have the effect of defunding the programs he has claimed to protect. Trump will not be on the ballot again, but the party he has remade in his image will have to contend with the fallout.

While the economy effectively absorbed the large number of both legal and undocumented migrants admitted under President Joe Biden, that surge created undeniable social strains in many of the cities where they concentrated. The broad backlash against that experience (even among many established immigrant communities) makes clear that maintaining a secure border, as Trump has achieved, must be the foundation of any politically viable immigration policy. But ensuring that immigration moves through legal channels is very different from narrowing or closing those channels altogether. Without a replenishing flow of immigration, the U.S. inexorably will grow older and smaller — and that isn’t likely to meet anyone’s definition of making America great.

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This column reflects the personal views of the author and does not necessarily reflect the opinion of the editorial board or Bloomberg LP and its owners.

Ronald Brownstein is a Bloomberg Opinion columnist covering politics and policy. He is a CNN analyst and the author or editor of seven books.

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