On Saturday, up to 3,000 of them, young and old and diverse, packed into this city’s largest venue to roar their support as the veteran senator and frontrunner argued this year’s was the most consequential election in modern history. He said the nation could not let Donald Trump serve another four years.

“The media at the back of the room is not just from America. It’s from around the world,” he said. “The world is watching if the people of Iowa are prepared to stand up for justice. The world is watching to see if the people of Iowa are prepared to create for an economy that helps all people, not just the one per cent.”

He added: “It all begins in Iowa, two days from now. And I’m here to ask you, very humbly, for your support on caucus night.”

The Democrat challengers to Trump in 2020 Show all 25 1 /25 The Democrat challengers to Trump in 2020 The Democrat challengers to Trump in 2020 Bernie Sanders The Vermont senator has launched a second bid for president after losing out to Hilary Clinton in the 2016 Democratic primaries. He is running on a similar platform of democratic socialist reform Getty The Democrat challengers to Trump in 2020 Joe Biden The former vice president recently faced scrutiny for inappropriate touching of women, but was thought to deal with the criticism well and has since maintained a front runner status in national polling EPA The Democrat challengers to Trump in 2020 Elizabeth Warren The Massachusetts senator is a progressive Democrat, and a major supporter of regulating Wall Street Reuters The Democrat challengers to Trump in 2020 Amy Klobuchar Klobuchar is a Minnesota senator who earned praise for her contribution to the Brett Kavanaugh hearings Getty The Democrat challengers to Trump in 2020 Michael Bloomberg Michael Bloomberg, a late addition to the 2020 race, announced his candidacy after months of speculation in November. He has launched a massive ad-buying campaign and issued an apology for the controversial "stop and frisk" programme that adversely impacted minority communities in New York City when he was mayor Getty Images The Democrat challengers to Trump in 2020 Tulsi Gabbard The Hawaii congresswoman announced her candidacy in January, but has faced tough questions on her past comments on LGBT+ rights and her stance on Syrian President Bashar al-Assad Getty The Democrat challengers to Trump in 2020 DROPPED OUT: Pete Buttigieg The centrist Indiana mayor and war veteran would be the first openly LGBT+ president in American history Getty The Democrat challengers to Trump in 2020 DROPPED OUT: Deval Patrick The former Massachusetts governor launched a late 2020 candidacy and received very little reception. With just a few short months until the first voters flock to the polls, the former governor is running as a centrist and believes he can unite the party's various voting blocs AFP/Getty The Democrat challengers to Trump in 2020 DROPPED OUT: Beto O'Rourke The former Texas congressman formally launched his bid for the presidency in March. He ran on a progressive platform, stating that the US is driven by "gross differences in opportunity and outcome" AP The Democrat challengers to Trump in 2020 DROPPED OUT: Kamala Harris The former California attorney general was introduced to the national stage during Jeff Sessions’ testimony. She has endorsed Medicare-for-all and proposed a major tax-credit for the middle class AFP/Getty The Democrat challengers to Trump in 2020 DROPPED OUT: Bill De Blasio The New York mayor announced his bid on 16 May 2019. He emerged in 2013 as a leading voice in the left wing of his party but struggled to build a national profile and has suffered a number of political setbacks in his time as mayor AFP/Getty The Democrat challengers to Trump in 2020 DROPPED OUT: Steve Bullock The Montana governor announced his bid on 14 May. He stated "We need to defeat Donald Trump in 2020 and defeat the corrupt system that lets campaign money drown out the people's voice, so we can finally make good on the promise of a fair shot for everyone." He also highlighted the fact that he won the governor's seat in a red [Republican] state Reuters The Democrat challengers to Trump in 2020 DROPPED OUT: Cory Booker The New Jersey Senator has focused on restoring kindness and civility in American politics throughout his campaign, though he has failed to secure the same level of support and fundraising as several other senators running for the White House in 2020 Getty The Democrat challengers to Trump in 2020 DROPPED OUT: Wayne Messam Mayor of the city of Miramar in the Miami metropolitan area, Wayne Messam said he intended to run on a progressive platform against the "broken" federal government. He favours gun regulations and was a signatory to a letter from some 400 mayors condemning President Trump's withdrawal from the Paris Climate Accord Vice News The Democrat challengers to Trump in 2020 DROPPED OUT: Kirsten Gillibrand The New York Senator formally announced her presidential bid in January, saying that “healthcare should be a right, not a privilege” Getty The Democrat challengers to Trump in 2020 DROPPED OUT: John Delaney The Maryland congressman was the first to launch his bid for presidency, making the announcement in 2017 AP The Democrat challengers to Trump in 2020 DROPPED OUT: Andrew Yang The entrepreneur announced his presidential candidacy by pledging that he would introduce a universal basic income of $1,000 a month to every American over the age of 18 Getty The Democrat challengers to Trump in 2020 DROPPED OUT: Julian Castro The former San Antonio mayor announced his candidacy in January and said that his running has a “special meaning” for the Latino community in the US Getty The Democrat challengers to Trump in 2020 DROPPED OUT: Marianne Williamson The author and spiritual adviser has announced her intention to run for president. She had previously run for congress as an independent in 2014 but was unsuccessful Getty The Democrat challengers to Trump in 2020 DROPPED OUT: Eric Swalwell One of the younger candidates, Swalwell has served on multiple committees in the House of Representatives. He intended to make gun control central to his campaign but dropped out after his team said it was clear there was no path to victory Getty The Democrat challengers to Trump in 2020 DROPPED OUT: Seth Moulton A Massachusetts congressman, Moulton is a former US soldier who is best known for trying to stop Nancy Pelosi from becoming speaker of the house. He dropped out of the race after not polling well in key states Getty The Democrat challengers to Trump in 2020 DROPPED OUT: Jay Inslee Inslee has been governor of Washington since 2013. His bid was centred around climate change AFP/Getty The Democrat challengers to Trump in 2020 DROPPED OUT: John Hickenlooper The former governor of Colorado aimed to sell himself as an effective leader who was open to compromise, but failed to make a splash on the national stage Getty The Democrat challengers to Trump in 2020 DROPPED OUT: Tim Ryan Ohio representative Tim Ryan ran on a campaign that hinged on his working class roots, though his messaging did not appear to resonate with voters Getty The Democrat challengers to Trump in 2020 DROPPED OUT: Tom Steyer Democratic presidential hopeful billionaire and philanthropist Tom Steyer is a longtime Democratic donor AFP/Getty

It might well have been the Vermont senator’s time four years ago. Written off by Hillary Clinton’s campaign virtually before the contest had started, he ran her to less than half a percentage point in Iowa, and went off to defeat her 60-37 in the second state to vote, New Hampshire. He continued to push her all the way into the summer, refusing to suspend his campaign.

Later it would emerge – thanks to emails apparently obtained by Russian hackers and published by Wikileaks – that some officials in the supposedly neutral Democratic National Committee (DNC) were supporting her, and working against him. The revelation further poisoned the relationship between the two camps, and Sanders’ relationship with the establishment of the party’s whose nomination he was seeking.

Four years on, Sanders’ raft of progressive policies are largely the same – he proposes universal healthcare, tuition-free college, the transition to a green, low-carbon economy, criminal justice reform and a federal minimum wage.

At the age of 78, his style on the stump – pointing, jabbing, his voice sometimes close to a growl – has not altered.

Yet two significant things have shifted. Firstly, in what already counts as victory for the one-time mayor of Burlington, a lot of his seemingly outlier policies have been adopted by many of the other candidates, as the position of progressives such as Alexandria Ocasio-Cortez and Ilhan Omar, the latter of whom was on the stage in Cedar Rapids, has become ascendant.

The second is that Sanders is no longer an unknown outsider: the most recent poll by The New York Times placed him in joint first place in Iowa with Joe Biden, and second nationally to the former vice president, followed by Elizabeth Warren and Pete Buttigieg.

Joe Rogan says he'll 'probably vote' for Bernie Sanders

Rebecca Hovde said one of the reasons she was there to show her support for the senator was because he had worked to expose the unfairly high costs being charged by a drug company for medicine she needs for a rare disease.

One in three million people suffer from Lambert-Eaton myasthenic syndrome (Lems), an autoimmune disorder that causes fatigue and weakness. While the pills, of which she requires four a day, cost just 10 cents to make and which she once received for free, Catalyst Pharmaceuticals, which bought the US rights to the drug, wanted to charge an annual sum of $375,000.

“He went to them and called them out,” said Hovde, who lives in Wellman, 50 miles from Cedar Rapids.

Aliah Rowe and Sara Ledesla, both 19, drove nine hours from Arkansas to attend the rally at the US Cellular Centre, which also featured a performance by the New York-based band Vampire Weekend.

“He is not owned by anyone. He is not doing it for himself,” said Rowe.

Ledesla claimed Sanders was the only candidate looking to build a diverse coalition that represents different parts of society. Both said they thought he could defeat Trump and that his age was not an issue.

Sanders raised more money than any of his Democratic rivals in the last quarter of 2019, and has invested heavily in a ground operation in Iowa, backed up by volunteers from across the nation. He claimed his supporters had knocked on 500,000 doors in Iowa alone. The state’s population is just 3.1 million.

Four years ago, a number of those attending Sanders’ events in Iowa and elsewhere suggested they would not support Clinton if she became the nominee. A number said their second choice would be Trump, whom they believed was similarly not-bought, and willing to tell the truth.

The antipathy towards Clinton remains. On Friday, another of Sanders supporters in the House of Representatives, Rashida Tlaib, led booing of Clinton at a campaign event in Clive, Iowa.

Yet few at Saturday’s rally, which also features an address by Cornell West, appeared to have any love for Trump. Rather, they said Democrats had unwisely underestimated him and that it was now vital to defeat him.