As the Senate takes up the “One Big Beautiful Bill” (Donald Trump’s name for it) passed by the House last week, there’s finally some discussion of the national debt. That’s because the bill is estimated to add $3.8 trillion over the next decade to the current debt: $37 trillion, or more than 120% of U.S. GDP.

The bond markets have been shouting their disapproval. Bond investors are demanding higher yields because they’re starting to doubt that we can be trusted to pay off our obligations. Interest on the debt in fiscal year 2025 will exceed spending on defense, Medicare and Medicaid. By 2035, it’s projected to overtake everything but Social Security.

I want to pull back the lens a bit.

The phrase “demography is destiny” is overused and abused, but there’s some truth to it. Consider Thomas Malthus. In “An Essay on the Principle of Population” (1798), the pioneering economist identified what came to be known as the “Malthusian trap.” In prosperous times, population grows geometrically but food supplies increase only arithmetically. More babies lead to fewer resources per person, eventually causing a population crash. Malthus gets a bad rap because he was broadly right retrospectively but profoundly wrong prospectively. In other words, he offered a serviceable rule of thumb about how demographics and economics had worked for thousands of years at the precise moment that rule was hitting its expiration date. Since 1800, humans have figured out how to increase food supplies to far outpace increases in population.

But if you were a policymaker in 1800, you’d have been a fool not to take Malthus seriously. The problem today, unlike in 1800, is that we’re in uncharted territory when it comes to the population-and-resources calculation. No society has gotten so rich and so old amid such a crash in fertility rates as ours. And while our debt is driven by many factors, it is the cost of entitlements, particularly for the elderly, that is by far the most serious across much of the rich world.

In 1940, when retirees first started receiving Social Security benefits, there were 42 workers per recipient. Today there are about 2.7 workers for every Social Security beneficiary. In Japan, the oldest nation in the world (where debt is above 255% of GDP), the number is 2.1. This trend applies across the developed world.

The primary reasons for it are pretty simple: We are making fewer babies and people are living a lot longer. In 1940, life expectancy at birth for American men was 61.4; for women it was 65.7. If you made it to 65, most people had about a dozen years left. Today life expectancy at birth is close to 80. Not only do more people reach 65, but when they do, they also can expect to live nearly 20 more years.

Oh, and contrary to a lot of political rhetoric about how Social Security payments are simply “your money” paid in to the system by you over a lifetime, a majority of beneficiaries receive far more than they paid in.

Of course, the imbalance between workers paying in and retirees isn’t just a challenge because of Social Security, but it’s telling that Social Security is the only program that is so expensive that it will continue to outpace interest payments on the debt if current trends hold — one reason why it’s projected to be insolvent in eight years. Medicare, the old-age healthcare program, is projected to be insolvent in 11 years. This leaves out the enormous private costs of an aging population. Many families spend vast sums on the last years of their parents’ lives.

Again, we don’t know how this will end because societies haven’t been here before. But if we do nothing, some kind of debt crisis seems inevitable. There are things politicians could do to mitigate the worst-case scenarios. Both the U.S. and Germany have incentivized later retirement to help mitigate the problem. But I for one do not find much comfort in the idea that our current politicians will suddenly find the wisdom and courage required to do much more.