The man behind the counter at the petrol station off the interstate in New Hampshire was probably working for just above minimum wage. He was wearing a “Donald Trump for President” badge, so I asked him: “What’s got you supporting Trump?”

“The guy knows how to run things,” he said.

“But he’s not exactly a friend of the working man,” I replied.

The man’s lips tightened. “You sound like someone supporting Sanders.”

“Actually, leaning towards Hillary,” I said.

He hesitated. “At least she’s not a socialist.”

It’s one of the stranger verities of US politics: the way that so many members of the beleaguered working and middle classes have become wary of any politician who talks about social democracy.

Anyone who wants to see a brilliant depiction of the predicament facing the American middle class should watch Stephen Karam’s play The Humans, recently transferred to the “Great White Way” (as Broadway is still called). The set-up is classic Americana: at a family Thanksgiving dinner, manifold disappointments and griefs are aired. Indeed, this is a family in which no one is doing particularly well; success has eluded even the high-achieving daughter (who is about to lose her job at a prestigious law firm because she hasn’t proved profitable). The other daughter, a once promising composer, is waiting tables to pay the rent on her dumpy New York apartment – and secretly pleased that her boyfriend has a small trust fund.

Their parents live in the blue-collar city of Scranton, Pennsylvania, a true rust-belt enclave on a downward curve, where they struggle to stay afloat in jobs (an office manager, a school electrician) that once would have given them a stable, middle-class lifestyle. But today, as the father notes, the price of everything is ruinously high.

What makes the play so potent is the way that Karam, without political platitudes or sweeping statements, captures a salient truth: the once great middle class – considered for generations the economic and social bedrock of the nation – is now in a largely forlorn state.

It was poignant to watch this play on my native island of Manhattan. I grew up here when there was a functioning middle class within its vertical geography. I remember this not-too-distant era (the Sixties and Seventies), when a schoolteacher, a producer for public radio and a fireman (to name just a few of our neighbours in the apartment building on West 77th Street) could live and even raise families in the city centre.

The Reaganite boom of the Eighties began to undermine Manhattan’s affordability, as Wall Street remunerations ballooned, pushing rents and real-estate prices into the stratosphere. The boom has yet to end. We have reached the point where, according to a recent New York Times article, someone making $250,000 a year in Manhattan is considered to be on “the upper edge of middle class”. More tellingly: “Household incomes in Manhattan are about as evenly distributed as they are in Bolivia or Sierra Leone – the wealthiest fifth of Manhattanites make 40 times more than the lowest fifth.”

Granted, Manhattan is not the American heartland and it boasts, with San Francisco, the most expensive cost of urban living in the country. This is nonetheless an accurate reflection of a larger statistical truth: there is a huge fiscal disparity between affluent Americans and their middle-class compatriots.

Consider this analysis from Mark Gongloff, writing in the Huffington Post after Barack Obama’s 2015 State of the Union address, in which the president asked Congress for tax hikes on the wealthy and cuts for those in middle-income brackets (a legislative outcome as likely as Elvis being discovered alive in Aleppo):

The only [income] boost middle- and low-income families have gotten since 1979 came during the tech boom of the 1990s. It’s been a Sea of Suck otherwise. For the richest Americans, wages have done nothing but climb . . . Meanwhile, costs that affect the middle class the most are outpacing paltry wage gains – particularly childcare and education.

Compare this to the booming postwar years, when the aspiration of having “a chicken in every pot and a car in every garage” was a realisable goal for the majority of middle-class Americans. We now live in a new gilded age of plutocracy and the middle class simply cannot keep economic pace. And yet, outside of certain metropolitan pockets, the majority of its struggling members remain loath to embrace the socialism-lite precepts of Bernie Sanders and still believe in the system as it stands.

This is one of the great ongoing ironies of US politics: the way in which the middle class may line up for centrist Democrats such as Clinton or Obama but fears those who are further to the left. Anything that smacks of fairer income distribution or a more equitable tax structure does not play well among a group that has so often bought in to the Republican notion that Obamacare, or making the wealthy contribute an extra 5 per cent per annum, is tantamount to state socialism.

Herein lies the Gordian knot of American politics: how to convince those on middle incomes to start voting for people who truly want to push for greater economic fairness. It is an unsolvable conundrum that makes the downward slide of America’s middle class even more infuriating and sad to witness.