The number of Democrats lining up to try to take on President Donald Trump as he seeks re-election is growing by the week. So who's running and what are their strengths and weaknesses?
This field of candidates promises to be the most diverse yet. It already has the most women running in US history.
The BBC's Anthony Zurcher casts his eye over them.
Who? Senator for California, 54-year-old attorney, mixed race
Anthony's take: Kamala Harris is the kind of Democrat who could stick around and prevail in what is sure to be a gruelling nomination battle. She is from California, which is rich in both primary delegates and fundraising dollars. As a woman, and from an ethnic minority, she is well positioned to capitalise on her party's growing diversity.
She has one of the most liberal voting records in the US Senate at a time when Democrats are leaning to the left, but she also has a background as a hard-nosed prosecutor.
That background may end up a vulnerability as well, given that some progressives have criticised her for failing to support California criminal justice reform efforts and pointed to her prosecutorial record as being insufficiently sensitive to the rights of the accused. She will have to walk a fine line to tout her accomplishments while justifying her decisions.
Ms Harris has only been on the national stage two years, and not every political neophyte can hold up under fire the way Mr Obama did in 2008. She will be tested in the coming months, but she starts the contest near the head of the pack.
Who? Another senator, this time from Massachusetts, a thorn in the side of big banks
Anthony's take: Elizabeth Warren has been a favourite of the progressive left since she emerged on the political scene to push for tougher regulation of the financial sector after the 2008 economic crash. During her time in the US Senate she became known for her hard-nosed interrogations of Wall Street executives and as an outspoken critic of income inequality.
That loyal base may be enough to rise to the top of a fractured Democratic presidential field - particularly if Vermont Senator Bernie Sanders, the other progressive star of the Senate, decides not to run.
The challenge for Ms Warren will be expanding her appeal beyond the already converted. She's an academic by training, having spent much of her adult career as a professor. Her campaign, however, is already emphasising her working-class upbringing over her educational pedigree, as a means of connecting her personal story to the activist government policies she supports.
Ms Warren will face the challenge of having to define her candidacy while taking fire from Donald Trump, who has repeatedly disparaged her past claims of native American heritage. Although she hardly mentions the president in speeches these days, she'll have to convince Democrats she won't be only the latest politician the president has belittled - and then defeated.
Who? New York senator who likes to emphasise she's a mother of two, the candidate most closely allied to #MeToo
Anthony's take: Announcing a presidential campaign on the Stephen Colbert Show may end up a cliché by the time the year is over, but credit Kirsten Gillibrand with being one of the first to try it.
The New York senator's decision to (almost) throw her hat into the ring isn't a huge shock.
She's long been positioning herself as one of the candidates most likely to capitalise on the #MeToo movement, and her pitch as someone who will "fight as hard for other people's kids as she would for her own" just might resonate.
Her steady march to 2020 hit a few bumps along the way, though. She angered some Democrats by quickly calling for Senator Al Franken's resignation after he faced sexual harassment charges. And she alienated Clinton loyalists by criticising Bill Clinton's handling of the Monica Lewinsky scandal.
These decisions could hurt her, even if she cites them as evidence that she matches her feminist rhetoric with action.
As a New Yorker, however, she can tap into a deep vein of campaign cash. She's young and charismatic. If she catches the wave of women voters that powered Democrats to victory last year, it just might carry her to the nomination.
Who? Mayor of San Antonio, Texas, from 2009 to 2014, aged 44 and served as housing secretary for President Obama
Anthony's take: It wasn't long ago that Julian Castro would have been considered a top-tier candidate for the Democratic presidential nomination. He was a well-regarded mayor of San Antonio, landed the keynote address at the 2012 Democratic National Convention and went on to a Cabinet position in the Obama administration.
Now, however, he may not even end up the most popular Texan in the race, if former congressman (and Democratic heartthrob) Beto O'Rourke decides to run. And there are other politicians - ones currently holding elective office or, like former Vice-President Joe Biden, with instant name recognition - who are generating more presidential buzz.
Even if Mr Castro isn't quite the rising star he used to be - and, quite honestly, he has never been a particularly compelling public speaker - he still has the potential to build a following in the race to come. He's a third-generation Mexican-American at a time when Democrats are desperate to engage the growing Latino population in the US. He's young at a time when many Democrats are seeking generational change.
As a moderate in a party moving to the left, however, he's got his work cut out for him.
Who? Born in America Samoa, aged 37, represents Hawaiian district in Congress
Anthony's take: Tulsi Gabbard, the first Hindi member of the US Congress, is a difficult candidate to characterise.
Most of the Hawaii congresswoman's views fit firmly in the Democratic Party's progressive camp. She was an early and outspoken supporter of Bernie Sanders' 2016 presidential campaign and has been an advocate of universal government-provided healthcare, raising the minimum wage and an anti-interventionist foreign policy.
The Iraq War veteran has drawn criticism, however, for meeting with Bashar al-Assad in January 2017 - after the Syrian president had been accused of repeatedly using poison gas on civilian populations. The daughter of a socially conservative politician and activist, Ms Gabbard may also draw the ire of Democratic voters for her past criticism of "homosexual extremists" and opposition to abortion rights and gay marriage.
She's also opposed the Iran nuclear deal and condemned "Islamic extremism" in language more reminiscent of a Republican candidate.
If Democrats are looking for a young, charismatic iconoclast - even if it means supporting someone whose views don't always match their own - then Ms Gabbard might have a shot. As Republicans will attest, stranger things have happened.
Who? Became a city mayor when still in his 20s and served in the Navy, first openly gay candidate
Anthony's take: Most stories published about Pete Buttigieg prominently mention that he is a Millennial - a member of the generation born between 1981 and 1996. That isn't by accident.
The South Bend, Indiana, mayor isn't the only Millennial in the 2020 race - Hawaii Congresswoman Tulsi Gabbard is also 37 - but Mr Buttigieg is positioning himself as a voice for the young. As he notes, his generation came of age in the aftermath of 9/11, were the ones who fought in subsequent US wars and struggled to establish a financial foothold amidst the wreckage of the 2008 economic collapse.
Where their aging parents, the postwar Baby Boomers, may not be as concerned about long-term impact of US policies, Mr Buttigieg says Millennials will have to deal with the fallout from today's crises for decades.
Mr Buttigieg enters the race with a unique resume. He's an openly gay veteran of the Afghanistan War and a Rhode Scholar. As mid-western mayor, he's shown he has voter appeal in a region that helped deliver the presidency to Donald Trump.
The march of time ensures Millennials will run things someday. A Buttigieg presidency is a long shot for 2020, but his candidacy is a sign of things to come.
Who? Son of an electrician, spent six years as congressman in Maryland.
Anthony's take: Delaney was officially the first entrant into the 2020 Democratic presidential field when he announced his candidacy in July 2017. The former tech entrepreneur has a platform that focuses on jobs, education and infrastructure and a return to bipartisan co-operation.
Who? A retired Army Major who was state senator in W Virginia, aged 48
Anthony's take: He may not have won his 2018 campaign for a House seat from West Virginia, but that didn't stop the former Army paratrooper from already announcing his presidential bid. He offers an unusual blend of economic populism, education advocacy and support for coal mining and gun rights.
Who? An entrepreneur, 44, born in New York to Taiwanese parents
Anthony's take: A technology entrepreneur who is proposing the US government pay a $1,000-a-month "freedom dividend" to all Americans between the ages of 18 and 64 as a form of universal basic income to cushion against fewer jobs due to increased automation.