On a warm Wednesday evening, just before sunset, a group of young socialists gathered in a converted factory in Bushwick to be branded. Those that weren’t already wearing Bernie For President gear formed a queue at the tables where two print-makers, using a silkscreen, were knocking out vests and bandanas, t-shirts and patches as fast as they could.

“It takes about twenty minutes between each colour, so you’ve gotta be at the party for at least an hour,” David Maddy told me. This was no hardship. The lights of the Chrysler building could be glimpsed in the distance across Brooklyn and the East River. There were Rolling Rocks to be had, two for five. The stereo played the KKK Took My Baby Away, a Ramones song released before most of the people at this informal campaign event were born.

Politics and politicians are so unpopular, even more so in the United States than in Britain, that left and right wing candidates invariably present themselves as revolutionaries. And sure enough, before the ink was dry on the first layer of Maddy’s vest, I had heard a promise to upend the political order. “Bernie’s campaign is about changing the way things are run. This is the first ever people’s campaign,” said Moumita Ahmed, a grassroots co-ordinator at People For Bernie.

Seven years ago, as a teenager, she cast her first vote for Barack Obama, another avowedly transformative presidential candidate. She had seen what the USA’s rotten political system does to hope and change, and invested her faith in Bernie Sanders, a seventy-three-year-old Jewish Senator from Vermont with a stoop and a gravelly voice and an eleven point plan to reduce inequality and make America great again. “I mean, I love Obama, but Bernie’s on another level,” she said. “And I’m not the only one.”

Later, she addressed the crowd: “everyone, if you’re tweeting, please use the hashtag #feelthebern.” The Sanders campaign is doing an excellent job of finding and connecting with supporters on social media. On Facebook, his page has 1.8 million ‘likes’ - 0.6 million more than Hillary Clinton. In a national Economist/YouGov poll last month, the two candidates were neck and neck among voters under thirty.

John Fahey, a thirty-one-year-old actor, was wearing a bright blue Bernie Is Bae t-shirt (apparently this is millennial slang for babe). “Bernie’s the first time I’ve been excited about a candidate,” he said. “I see him as someone in politics that has integrity and a moral compass that isn’t changing from decade to decade or day to day.”

This is a crucial element of the Sanders pitch. He has been fighting the same injustices and advocating the same remedies ever since he first ran for office, representing a fringe party that was founded to oppose the war in Vietnam. After four heavy defeats, he was elected Mayor of Burlington in 1981, and since 1989 he has served Vermont, as the state’s only Congressman and then as a Senator. He calls himself a socialist, but has caucused with the Democratic party on Capitol Hill, more or less reliably.

In recent years, many of his positions that were once radical have become mainstream. Under the Clinton administration, he voted against the Defence of Marriage Act that defined marriage as between a man and a woman, two decades before it was dismantled by the Supreme Court. Under George W. Bush, he opposed the Patriot Act, long before Edward Snowden’s revelations cause Americans to think twice about the government hoovering up personal data in the name of security. He fought the Clinton-era deregulation of Wall Street and argued against invading Iraq when almost everyone else in Congress was for it.

The millennials at the party were socialists of a European stripe, willing to pay high taxes to fund a generous welfare state. But in most of the United States, outside New York and Seattle, Portland and Los Angeles, socialism means communism means Stalin. There aren’t many worse insults you can throw at a politician.

In June, a Gallup poll found that nine in ten Americans would vote for a black, Hispanic, Catholic or Jewish candidate for president. Seven in ten would vote for a homosexual, six in ten for a Muslim. Fewer than half would vote for a socialist. In 2008, Obama’s bland observation that “when you spread the wealth around, it's good for everybody” became one of John McCain’s most effective attack lines.

If elected, Sanders promises to raise the federal minimum wage to $15 an hour, break up the most powerful banks, eliminate tax loopholes that benefit corporations, create a single-payer, free-for-all health service modelled on the Medicare programme for senior citizens, end the ‘war on drugs,’ reduce the number of people in prison, invest billions in infrastructure and introduce free university education for anyone that wants it.

“He’s not using fluff words. He has an eleven point plan and they’re very specific,” Maddy told me. “Hillary says ‘we have some problems and we need to address them.’ Well, now’s your chance - address them, say something. He’s the only candidate on the left that’s presenting something concrete.”

This old-fashioned social democratic platform, wildly ambitious by modern standards, is dependent on raising taxes, primarily but not exclusively on the wealthy, and for this reason Washington insiders and the establishment media think a Sanders victory is as likely as an iceberg in the Caribbean. There’s also the inconvenient fact that he doesn’t have the declared support of a single member of Congress.

Sanders has attracted eye-catching crowds at his rallies - at least 19,000 people in Portland, 15,000 in Los Angeles, 12,000 in Seattle and 11,000 in Phoenix - but at the moment his support is strongest in white, liberal areas. “A lot of people don’t know who he is,” admitted Maddy. “I went around this past weekend registering voters in African-American and Latin-American neighbourhoods not far from here, and a lot of those people do not know who he is.”

Jon Fuhrer, the party’s host and a seasoned political activist, told me: “Bernie can only beat Hillary because of his grassroots energy. We need to be effective organisers. So when we’re going into a hipster place or an area that’s very progressive, we’re not going to be as effective as we are going into an area where he’s only known by a third of people.” He passed me a flyer in Spanish.

Last month, Black Lives Matter activists shut down a Sanders event in Seattle. For days, a debate raged online about whether Sanders takes racial justice seriously and whether his policies would benefit ethnic minorities. “Hillary’s strategy is capturing the centrist vote and the black and Latino vote, because Bernie has such low name recognition and he comes from a state that’s very white,” said Fuhrer. “That’s why her surrogates are pitching to the media that Bernie has a supposed black problem. But if we’re out in the field and actually talking to voters we can break through that.”

Sanders is a dangerous opponent for Clinton, the ultimate establishment candidate and an arch triangulator who was for the Iraq war and the ‘war on drugs’ before she was against them. Since the revelation that she used a personal email server while she was Secretary of State, her popularity ratings have dropped - she’s now viewed favourably by 42% of voters and unfavourably by 48%. Nate Silver, the USA’s reigning political prognosticator, still gives her an 85% chance of winning the Democratic nomination, but it’s not a foregone conclusion.

One intriguing question is who Elizabeth Warren will endorse. Many on the left wing of the party were sorely disappointed when the Senator from Massachusetts decided not to run herself. “I love what Bernie is talking about,” she told the Boston Herald, but she has also expressed her admiration for Clinton.

On July 29, Sanders made a pitch to the unions, telling representatives of the AFL-CIO (equivalent to the TUC) that his opposition to the proposed Trans-Pacific Partnership showed that he is the candidate most likely to advance the interests of organised labour. The American Federation of Teachers has endorsed Clinton.

The primary calendar suits Sanders, in that the first two states to go to the polls, Iowa and New Hampshire, are both predominantly white, and small enough for a cash poor campaign to compete. Sanders has been gaining support, particularly in New Hampshire: according to the Huffpost poll aggregator he is currently tied with Clinton at 42%. His campaign hopes that a strong showing in the early contests and in the six Democratic presidential debates will introduce him to voters.

Sanders has never run an attack ad, and he rejects the help of so-called Super PACs that allow wealthy individuals and corporations to spend unlimited amounts on campaigns. This principled position is central to his appeal, but it also makes it impossible to match Clinton on the ground or over the airwaves. She will need to be careful about attacking him - opponents in Congressional races have found him to be a master of political jiu-jitsu, capable of using their strengths against them - but her logistical advantage is overwhelming.

“He has no operations in South Carolina and Nevada at this point, let alone forty-six other states. Hillary has so much more money that she can hire organisers and directors and co-ordinators in these states ahead of time,” Fuhrer admitted.

During the 2007-8 Democratic primaries, Obama often pointed out that his campaign was largely funded by small donations. He also took more than $1 million from employees of Goldman Sachs and $20 million from the private healthcare industry. Sanders will be reliant on his volunteers to a degree unprecedented in the modern era.

“Obama was very much an establishment Democrat who had a different message, and he had a great campaign, but ultimately he was taking Wall Street money, he was taking corporate money, he had a lot of elected officials in the Democratic Party machine backing him,” said Fuhrer. “Bernie is a straight up outsider who has been bucking the trend for a long time.

As we spoke, we were constantly interrupted by people wanting to buy beer and t-shirts. An older man with white hair wandered in. “I actually don’t know anything about Bernie Sanders,” he said, diverting Fuhrer’s attention for good. There was canvassing in East New York to organise, Twitter and Facebook to feed, a list of neighbourhood block parties to visit on Saturday. Although he admitted that Sanders faces long odds, Fuhrer was adamant: “he can win”.