One in five US adults now lives in households either in poverty or on the cusp of poverty, with almost 5.7m having joined the country's lowest income ranks since the global financial crisis.

Many of the new poor, or near-poor, have become so even amid an economic recovery that is widely expected to lead the US Federal Reserve to raise interest rates next week for the first time in almost a decade. More than 45 percent of them — almost 2.5m adults — have joined the lowest income ranks since 2011, long after the post-crisis recession was ostensibly over.

The findings, contained in data prepared for a new study of the US middle class by the Pew Research Center and shared with the Financial Times, put a stark human face on the economic legacy left by the crisis and reveal how uneven the recovery has been.

They illustrate how many Americans are being left behind even amid the strong jobs growth that, should the Fed move as expected, will be at the core of the argument its policymakers present for raising rates.

They also help explain why any notion of a recovery still seems a long way off to many in the US and why the message of populist politicians such as Donald Trump that America is not working resonate on the eve of an election year.

"There's a new American dream," says Torrey Easler, a Baptist preacher who helps feed a growing population of poor in the town of Eden, North Carolina. “The old American dream was to own a home and two cars. The new American dream is to have a job.”

A large part of the shrinking of the US middle class, which for the first time in decades now forms less than a majority of the country's adult population, has surprisingly been due to the country's growing affluence, the Pew study found.

But the country's lowest income group — defined by Pew for a three-person household as earning less than $31,402 a year — has also grown at more than five times the rate of the middle class in the past seven years. There are now 48.9m adults in this bracket in the US, up from 43.2m in 2008 and just 21.6m in 1971.

Kathryn Edin, a Johns Hopkins University sociologist who authored a recent book about those living on less than $2 a day in the US, argues that the shrinking social safety net after landmark 1990s welfare reforms has made the US a harsher place to be poor than it was.

The offshoring or automation of many low-skilled jobs has also made rising out of poverty harder than it once was, she says: "The bad jobs of yesterday were just much, much better than the bad jobs of today."

The educational make-up of the middle class has also changed significantly. In 1971, 76 percent of adults in middle class households had a high-school education or less. Today that figure is just 40 percent, according to Pew's data analysis, while just 12 percent of adults in lower income households had a university degree.

"It's a tough world out there when you get into these very competitive, knowledge-based, very up and down, transient businesses that are here today and gone tomorrow," says Robert Doar, a former New York City social services commissioner and now a fellow at the conservative American Enterprise Institute. “But that's not what the problem is at the bottom. The problem for people at the bottom is that they can't get up and be in that game.”