For a man who supposedly cannot win, Bernie Sanders is doing pretty nicely. Even his opponents in the Hillary Clinton camp have been forced to concede that much. Yet as America’s presidential primary season grinds on and the nation looks ahead to the party conventions in July, it is time to admit something more. Stand aside, Donald Trump: the big story of the 2016 US presidential election, underplayed and under-reported until now, is the extraordinary rise of Sanders.

He has gone from being a joke – a socialist! From Vermont! – to getting the full blowtorch treatment from the Democratic establishment, which sees him now as less of a batty uncle than a Bond villain. As the Nobel Prize-winning economist and New York Times columnist Paul Krugman asked last week: “Is Mr Sanders positioning himself to join the ‘Bernie or bust’ crowd, walking away if he can’t pull off an extraordinary upset, and possibly helping put Donald Trump or Ted Cruz in the White House? If not, what does he think he’s doing?”

Well, just campaigning, really. Sanders had said that Hillary Clinton was unqualified to be president, which is a tough thing to say, and may or may not be true, but in this year of all years (think of the Republican fight over the wives of Trump and Cruz; think, if you can bear it, of The Donald’s penis) it’s hardly World War III.

What has most upset the Hillary crowd is the horrid inconvenience of Sanders. The media, too (what on Earth is the point of political punditry after this campaign season?), have underestimated and patronised the Vermonter. An elderly, eccentric Jewish man from a picture-postcard state so outside the American mainstream that advertising billboards are banned there was hardly going to go the distance. He would fade. He’d get sweaty in the Deep South and lost in the hugeness of the Midwest. He would pine for the trees and cows and greenery of his home state. Clinton would crush him.

Well, it hasn’t happened. Sanders has already made history, ripping up the campaign rule books which say that once you begin to be seen as a loser, you’re toast. Sanders is still widely (if wrongly; more on which later) seen as incapable of beating Clinton, but his ability to raise funds, the lifeblood of any presidential push, has been undiminished.

In fact, the grey-haired socialist turns out to be a money magnet. On one day in February – one day – he raised $6m. Every month this year he has raised more than Clinton. Let’s just think about that. She is widely touted as the eventual winner. She has elite, premium-grade access to the drinks cabinet in every boardroom in America. She is (did she mention this?) the first woman with a credible chance of winning. But she can’t match his dough. Sanders raised $44m in March, almost $15m more than she did.

There is worse news still for the Hillary camp. While she raised most of her money from people giving the maximum legal amount for an individual donor – $2,700 – he raised most of his from folks giving hardly anything. The average gift to Sanders is just $27, but millions are doing it, so the zeros look after themselves. In fact, he has made more money from small donations than Barack Obama managed in 2008. He is the first serious candidate to refuse to work with a super-Pac: a fundraising body, separate from a candidate’s campaign, which can spend corporate cash on his or her message.

This money-magnetism has implications in both the short and the long term. It keeps Sanders’s candidacy alive almost irrespective of how he performs in primary contests. If he carries on raising money like this he can last through to the July convention and harass Clinton all the way.

Second, it points the way for other left-wing candidates in the future: it is possible to make a serious run for the presidency in the modern United States without corporate money. That is an enticing prospect for an ambitious mayor of a large city who wants to bring high minimum wages and public transport and gun control to the whole nation. In other words, Sanders has managed to start a revolution that could end – even if he fails – in a genuinely left-wing Democratic candidate succeeding one day.

That is quite a change, and one that ought to be noticed on this side of the Atlantic, too, by politicians of all stripes desperate to reconstruct mass parties for the modern age. True, American culture, on both the left and the right, makes people less cynical than we are about giving to political causes. What works in Detroit might not work in Doncaster. But the Sanders numbers will surely be watched in British party HQs.

Wait, cry the Hillary people: even if all that might be true, Sanders is losing in delegates to the party convention. She has won more than he has, and that’s that.

Clinton is ahead in elected delegates, but not by a huge number. She is relying on the so-called super-delegates, the party bigwigs, to see her home and dry. The Democratic Party invented this oligarchic system precisely to keep the left – the unelectable left – out. But Sanders is electable. In poll match-ups he beats all the possible Republican candidates. What right has the Democratic Party to bar him by using its unelected officeholders?

So, could he still win? A loss for Clinton in New York State would hurt her badly (the primary is on 19 April). So would an ­indictment from the FBI over her state department emails. A health scare? Something Bill does or says?

And then it would be Sanders v Cruz or Trump. My choice would be Sanders v Cruz: Vermont v Texas. For Americans who have been waiting for it, a true clash of civilisations. And no need to leave home.

Justin Webb is a presenter of Radio 4’s “Today” programme and a former North America editor for the BBC