And so the Democratic race to become the 2020 presidential nominee reaches two dozen, or 23 depending on how seriously you take all of the candidates. It is the largest field in modern history.

The Democrat races for the 1972 and 1976 elections both topped out at 16, and there were 17 Republicans as Donald Trump began his march towards the White House in 2016.

New York mayor Bill de Blasio is the latest to enter the race this time around, hoping to become the first mayor to gain the presidency.

The closest a mayor has come was in 1812 when DeWitt Clinton – who was also from New York – lost to James Madison in the general election.

It is not just that piece of history De Blasio is fighting – the crowded field means that making it through to become the party’s nominee will be unlike any other race.

So why is the field so stocked for 2020?

Well, as you might expect, some of it has to do with the current president. Trump ran a populist campaign with hard lines on immigration, crime and healthcare that have riled politicians and would-be politicians across the spectrum. That has brought more people to the table to fight him.

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

In his announcement, De Blasio said Trump was “a bully” who he knew how to fight. Such claims have been typical of the Democratic field.

“It’s an election that, for Democrats, has a sense of urgency,” Julian Zelizer, professor of history and public affairs at Princeton University, told Bloomberg recently.

“It’s a historic election. The sense of the risks of a second Trump term are great, so that’s going to inspire more Democrats than usual to go through what’s a brutal process: running for president.”

Trump also offers hope from an insurgent campaign perspective.

He did not enter the race until June the year before the 2016 election – but he drove to the top of the candidate standings very quickly. We still have at least three weeks until we reach the same point in this campaign.

As well as putting in his own money, he also ended up bringing in 69 per cent of his individual donations from small donors giving $200 or less by election time.

It is this type of funding that can keep smaller Democrat candidates, who cannot pull in big donations, in the race for longer.

Indeed, the Democratic National Committee’s rules for the first of the party’s debates on 26 and 27 May push candidates towards this. To qualify for one of the 20 spots over two nights, candidates must receive contributions from 65,000 unique donors across 20 states or have at least 1 per cent support in several public polls.

The fundraising may be easier, with some candidates struggling to get pollsters to put their names on the lists of surveys and others polling at essentially 0 per cent. This plays into the larger point that the barriers for entry to the national race are so much lower than they used to be. Campaigners are able to take their message to the people without support from big broadcasters.

Joe Biden launches his 2020 presidential campaign

With networks stretched for the staff needed to cover events from 20+ candidates across multiple states, the use of Twitter, Facebook videos and adverts and other social media strategies can have a bigger impact.

Indiana mayor Pete Buttigieg is a case in point. He received the most interactions on Twitter over a 30-day period into April and, while he has been helped by the reaction to a CNN-broadcast town hall event, social media has no doubt helped his cause.

Another example is Julian Castro, a former housing and urban development secretary in the Obama administration, who spent nearly a quarter of his operating expenses during the January-to-March fundraising period on digital ads, Federal Election Commission records show.

However, social media can be an echo chamber. Buttigieg admitted at an event in South Carolina earlier this month that he “needs help” reaching black vote – which he will need to make an impact – with some polls placing him at 0 per cent support with African-Americans in the state.

But in the records for the last funding window of January to March, Buttigieg and even less well-known candidate Marianne Williamson – who offers a “spiritual manifesto” – raised 64 and 60 per cent of their donations respectively from small donors.

That puts them behind only Bernie Sanders, Elizabeth Warren and Andrew Yang on that metric. In a field that won’t likely be cut significantly until February or March 2020, that can keep them in the race.

There have always been issue candidates, the most extreme this year being Mike Gravel, who at 88 merely wants to get on to the debate stage to highlight a non-interventionist foreign policy, direct democracy, and universal health care.

His campaign is being run by a 17-year-old and is not being taken terribly seriously. But, given the fractured political climate, other candidates are happy to ride the wave of one issue.

Washington governor Jay Inslee is concentrating on climate change, while Eric Swalwell is concerned with gun violence.

All it takes is one tweet, or short clip and you can pick up momentum for days. In decades past, this would have been thanks to a soundbite on television. Nowadays, TV will come to you once the message is shared enough via other channels first.