That means that as people reach their mid-60s, they have to either dramatically curtail their spending or keep working to survive. “This will be the first time that we have a lot of people who find themselves downwardly mobile as they grow older,” Diane Oakley, the executive director of the National Institute on Retirement Security, told me. “They’re going to go from being near-poor to poor.”

The problem is growing as more Baby Boomers reach retirement age—8,000 to 10,000 Americans turn 65 every day, according to Kevin Prindiville, the executive director of Justice in Aging, a nonprofit that addresses senior poverty. Older Americans were the only demographic for whom poverty rates increased in a statistically significant way from 2015 to 2016, according to Census Bureau data. While poverty fell among people 18 and under and people 18 to 64 from 2015 to 2016, it rose to 14.5 percent for people over 65, according to the Census Bureau’s Supplemental Poverty Measure, which is considered a more accurate measure of poverty because it takes into account health-care costs and other big expenses. “In the early decades of our work, we were serving communities that had been poor when they were younger,” Prindiville told me. “Increasingly, we’re seeing folks who are becoming poor for the first time in old age.”

This presents a worrying preview of what could befall millions of workers who will retire in the coming decades. If today’s seniors are struggling with retirement savings, what will become of the people of working age today, many of whom hold unsteady jobs and have patchwork incomes that leave little room for retirement savings? The current wave of senior poverty could just be the beginning. Two-thirds of Americans don’t contribute any money to a 401(k) or other retirement account, according to Census Bureau researchers. And this could have larger implications for the economy. If today’s middle-class households curtail their spending when they retire, the whole economy could suffer.

The retirement-savings system in the United States has three pillars: Social Security, employer-sponsored pensions or retirement-savings plans, and individual savings. But with the rise of less stable jobs and the decline of pensions, a larger share of older Americans are relying only on Social Security, without either of the two other pillars to contribute to their finances. This by definition means they have less money than they did when they were working: Social Security replaces only about 40 percent of an average wage earner’s income when they retire, while financial advisers say that retirees need at least 70 percent of their preretirement earnings to live comfortably.

Today’s seniors are so reliant on Social Security in part because companies that once provided pensions began, in the ’70s, to turn the responsibility of retirement saving over to individuals. Rather than “defined benefit” plans, in which people are guaranteed a certain amount of money every year in retirement, they receive “defined contribution” plans, which means the employer sets aside a certain amount of money per year. This switch saved companies money because it asked employees, not employers, to take on the risks associated with long-term investing. This means that the amount people receive is more affected by the ups and downs of the stock market, their individual wages, and interest rates. In 1979, 28 percent of private-sector workers had participated in defined-benefit retirement plans—by 2014, just 2 percent did, according to the Employee Benefit Research Institute, a nonprofit. By contrast, 7 percent of private-sector workers participated in defined-contribution plans in 1979—by 2014, 34 percent did.