Now I know what it’s like to Feel the Bern. During a week in New Hampshire culminating in his 22-point victory over Hillary Clinton on Tuesday, I saw Bernie Sanders in action, and it’s quite something. The talk of a movement is not exaggerated. His followers – many, but not all, young – are ready to walk through snowstorms to wave signs, hand out T-shirts and cheer themselves hoarse at his every sentence.

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And you can see why. He might be old, with the Larry David demeanour of a crotchety Jewish uncle, but he is a formidable speaker. He makes statements of fact that, together, add up to a case both morally indisputable and exhilarating for being so rarely voiced out loud. “The economy is rigged,” he says, incandescent that the US is now marked by the most unequal distribution of wealth and income since 1928.

The top 0.1% have greater wealth than 90% of the American people combined. There are 20 individuals – twenty! – who own more than the bottom 50%. A single family – the Waltons, owners of Walmart – own more wealth than the bottom 40%. Indeed, the Waltons are America’s “biggest welfare recipients”, because the low wages they pay their employees have to be topped up by benefits paid for by taxpayers. Or, as Sanders puts it: The Walton family are “down to their last 60 or 70 billion and you’re chipping in to help.”

The most powerful moments come when he involves his audience. He asks how many are burdened by student debt. A forest of hands goes up. One young woman, still at college, leaps to her feet to say she already owes $131,000. Another, doing a graduate degree at Columbia, is $200,000 in the red. Bernie adds from the podium that he knows of a dentist who owes $400,000, all “for the crime of getting an education”.

He runs a similar exercise with health insurance, asking people how much they are paying out in “deductibles”. For a non-American, especially anyone who takes Britain’s NHS for granted, the figures shouted out – in the high thousands – make the jaw drop. Sanders explains that when medical bills are that high, people hesitate to see the doctor and so “they get sicker”.

Prescription drugs cost so much because Big Pharma gives big bucks to the politicians in the form of campaign contributions, so Congress never acts to bring down the price of medicine. “Democracy is not about billionaires buying elections. That is oligarchy and together we are going to end it.”All this resonates deeply with his audience. When Sanders talks about people doing two or even three jobs to pay the bills, the semi-retired teacher next to me nods and murmurs that her son does exactly that. Sanders harks back to the era when one person, usually the man, could work a 40-hour week and provide for his whole family. When he promises to create an economy that works for working families and not just the top 1%, the room erupts.

Inevitably, British observers have drawn comparisons with Labour’s leader, Jeremy Corbyn. Yet Sanders struck a chord with me that Corbyn never has. Part of the explanation is that the Vermont senator is simply a much better speaker, capable of a crisp, ringing sentence. From his choice of campaign song – the stirring and now retro-chic America by Simon & Garfunkel – through to his latest, exceptionally moving campaign ad featuring the daughter of Eric Garner, the African-American killed by New York police whose last words were “I can’t breathe”, his campaign is highly accomplished.

Part of it is that Sanders does not carry the same baggage that weighs down Corbyn (though he has some serious luggage of his own). In some ways he is more radical than the Labour leader: both his analysis and proposals are bolder and more sweeping, even if he is a little hazy on how all this will get through a Republican Congress and be paid for. But no one has yet been able to question his patriotism. He sings the national anthem.

On foreign policy, the area that appears to animate Corbyn most, the sharpest accusation against Sanders is that he doesn’t really have one. It means that the senator is not burdened by a record of apparent indulgence of, or at least ambiguous statements about, terrorist groups. He has not had to clarify that, yes, he would approve of shooting Isis gunmen engaged in a killing spree after first seeming hesitant on that score. He does not have to defend a world view that seems forgiving of assorted dictatorships, so long as those dictatorships are hostile to the west.

The sharpest objection to Sanders is lodged against Corbyn: that he is unelectable. In the US, that case remains strong

The sharpest objection to Sanders is one regularly lodged against Corbyn: that he is unelectable. In America, that case remains strong. Sanders will be 75 in September, and Americans have tended to snub older candidates. What’s more, whichever Republican opponent Sanders faces will never let him forget that he is a self-described socialist, embracing a word that in the US is associated chiefly with the USSR during the cold war. A bombardment of TV ads will suggest that Sanders wishes to turn America into East Germany.

But the electability question is no longer as straightforward in my mind as it once was. That’s chiefly because his rival for the Democratic nomination, Hillary Clinton, is hardly a shoo-in. Exit polls from New Hampshire showed deep misgivings, even among Democrats, about Clinton’s honesty and trustworthiness. The saga of her use of a private email server and her decades-long habit of holding information back, only to release it eventually, has renewed that distrust.

She is a capable rather than inspirational candidate. And her close ties to Wall Street, including receipt of hefty speaker fees from Goldman Sachs, have put her on the wrong side of the anti-corporate wave currently carrying both Sanders and Donald Trump (who, like Sanders, boasts that he doesn’t need the big donors’ money, and so can’t be bought).

Add to that both the changing nature of the US electorate – whose demographic profile increasingly favours Democrats over Republicans in national elections – and the wild unpredictability of the voters’ mood in this year of anger, and it seems unwise to be too adamant about declaring anybody unelectable. Right now, in America, anything seems possible. Given our electoral system and the parliamentary arithmetic, that seems much less true of the UK.

Facebook Twitter Pinterest ‘In 2000, there was much excitement in progressive circles about Ralph Nader. Some of the same people buzzing about Bernie now were nuts about Nader then.’ Photograph: Keith Srakocic/AP

I know some people recoil from this talk of electability, seeing it as inherently unprincipled, even cynical. But here’s why I feel it so keenly. In 2000, there was much excitement in progressive circles about Ralph Nader. Some of the same people buzzing about Bernie now were nuts about Nader then. Meanwhile, Nader’s critics on the left said he would never be elected and that by fighting Al Gore in close states like Florida, he was only splitting the progressive vote and opening the door to George W Bush. And so it turned out.

Of course, running as a Democrat rather than a third party candidate is very different. But the point remains. Making Bernie Sanders the Democratic nominee would be an transformative statement, redrawing the boundaries of what’s possible in American politics. But if it makes it more likely that, come 8 November, the Republican party will control both the White House and the Congress, then that too will reshape the landscape – and not in a good way.

I have felt the Bern. And yet if the fire lit by this extraordinary, inspiring campaign ends up handing the Oval Office to Donald Trump, who would ban all Muslims from entering the US, or Ted Cruz, who wants to carpet-bomb the Middle East until it will “glow in the dark”, then Sanders-mania may exact a very high price. That is the calculation America’s liberal and progressive voters now need to make – and much more than the fate of their own country is at stake.