The 2020 field of Democrats who lined up to take on Donald Trump smashed records.
It was the most racially diverse field, the field with the most female candidates and the only field to include an openly gay candidate in the top contenders.
And now there are just three days to go until voters will finally get a chance to have their say.
There are still 12 candidates in the race, but there are clear frontrunners for the nomination.
We're going to split the remaining candidates into two criteria:
- Those who qualified for the last Democratic debate
- Those who didn't.
It'll give you a good idea of who you should be paying attention to. We'll list the frontrunners in alphabetical order below, or you can tap to jump to a particular candidate.
The frontrunners
Who is he?
The 76-year-old is the former vice-president of the United States and before that, US senator from Delaware. Mr Biden boasts one of the longest resumes of anyone in the 2020 race with a national political career spanning more than 45 years.
Mr Biden previously ran for president in 1988 and 2008 before becoming former US president Barack Obama's running mate.
What's his platform?
Mr Biden launched his campaign by invoking the 2017 violence in Charlottesville, Virginia, and President Donald Trump's response to it. The message was clear: I'm not Donald Trump.
As the campaign has developed, he modified that message slightly: I'm the only one who can beat Donald Trump.
Mr Biden has been the moderate standard bearer, and is considered to be close to the Democratic Party establishment.
His campaign before Iowa in one line
Mr Biden has led national poll after national poll since he made his announcement, but he's almost flown under the radar as multiple challengers have captured the spotlighted and faded away.
How will I remember him?
He probably won't wear them on the debate stage, but look out for Mr Biden's signature aviator sunglasses on the campaign trial. The shades, which he claims to have worn since he was 15, have become such an integral part of the Biden brand that the former vice-president claims people keep stealing them for souvenirs.
Who is he?
The gay, 37-year-old Mayor of a 100,000-person town in South Bend, Indiana. Former president Barack Obama once said Mr Buttigieg was the future of the Democratic party.
Mr Buttigieg (pronounced "Boot-edge-edge") has been credited with revitalising the Midwestern city's crumbling infrastructure and economy. He took leave from his mayoral term to serve in Afghanistan.
What's his platform?
Mr Buttigieg burst onto the stage with a bit of a blank slate when it came to national policy.
But as the race went on he found success by pitching a moderate policy platform like Joe Biden and Amy Klobuchar, most notably on the issue that defined the split between the candidates — healthcare.
His campaign before Iowa in one line
Mr Buttigieg went from an unknown mayor to a genuine top four contender but his campaign couldn't make several polling bounces permanent, meaning that Iowa is probably make or break for him.
How will I remember him?
His surname! It's so hard to pronounce that he turned it into merchandise for his campaign.
Speaking of things that are hard to pronounce, Mr Buttigieg himself is a polyglot, speaking French, Spanish, Italian, Norwegian, Maltese, Arabic and Dari.
Who is she?
The 58-year-old Minnesota senator was a lawyer before seeking public office. Senator Klobuchar drew widespread praise for her questioning during the recent nomination hearings of Supreme Court Justice Brett Kavanaugh.
What's her platform?
Senator Klobuchar is a moderate Democrat known for her pragmatism and hails from the Midwest, a group of states that flipped to Donald Trump in 2016 but Democrats will look to win back in 2020.
Her pitch? I can appeal to several key midwestern states that could define the 2020 election.
Her key policy to date is a trillion dollar infrastructure plan she's pledged to implement in her first year of presidency. The plan seeks to repair and replace roads and highways, expand public transport, and connect every home to the internet by 2022.
Her campaign before Iowa in one sentence
In a tumultuous campaign Senator Klobuchar has been steady as she goes — never finding a breakout moment but always keeping enough support to stay on the debate stage.
How will I remember her?
Senator Klobuchar won't be a stranger to the rigours of the road for the 2020 presidential campaign. She makes a point of visiting all 87 counties in Minnesota every year.
Who is he?
A senator from Vermont who, despite seeking the nomination of the Democratic party, is the longest-serving independent in US history. The 77-year-old was mayor of Burlington, Vermont before rising to the House of Representatives in 1990. He was elected to the US Senate in 2006.
What's his platform?
Senator Sanders is a self-described democratic socialist, making him the most left-leaning candidate in the race.
He has focused his campaign on economic issues, including Medicare for All, a $15 minimum wage, expanding the estate tax, limiting the size of banks, and tuition-free college.
He's also promised to pass a Green New Deal that would ban fracking and new fossil fuel infrastructure, end US exports of coal, natural gas and crude oil and move the US energy system away from fossil fuels.
His campaign before Iowa in one sentence
Sanders's core group of supporters have shown they're remarkably loyal (even through a heart attack) and he looks to be peaking at the right time, with polls showing him surging right before voters head to the polls for the first time.
How will I remember him?
He's yet to belt out a tune on the campaign trail, but Senator Sanders recorded a folk album, titled 'We Shall Overcome', in 1987 with 30 musicians.
It's less Beyonce and more Shatner. Even Senator Sanders himself called it "the worst album ever recorded" while on the campaign trail in 2016.
Who is she?
A senator from Massachusetts, who, rumour has it, considered a presidential run in 2016.
Before taking office, Senator Warren was a law professor who researched financial pressures facing middle class families. She served on a congressional oversight panel regarding the 2008 economic recession and as a special advisor to the treasury secretary.
And before that, the 69-year-old was a special-needs public school teacher and a full-time mum.
What's her platform?
She's not a socialist, but not quite a capitalist. You might call her a left-wing populist. Talk of taxing the rich and supporting the middle class are her rhetorical touchstones and they've been both a help and a hindrance in this campaign so far.
Some say Senator Warren has the most comprehensive policy positions of all the candidates. Her library of plans includes everything from immigration and healthcare reform to improving military housing and addressing maternal mortality.
Her campaign before Iowa in one sentence
Looked extremely promising at one point in the campaign, but has seriously struggled for momentum in recent weeks as the progressive vote swung behind Bernie Sanders and moderates firmed in behind Joe Biden.
How will I remember her?
You can thank Senator Warren for the feminist battle cry: "Nevertheless, she persisted." What now adorns coffee mugs, T-shirts and posters was first uttered in reference to Ms Warren by Republican Senate Majority Leader Mitch McConnell.
Senator Warren was warned not to argue against the nomination of former attorney-general Jeff Sessions by reading a letter from Martin Luther King Jr's widow. Nevertheless, she persisted, only to be voted off the floor.
Who is he?
An entrepreneur who found financial success running an education company and has never held elected office.
One of the youngest candidates in the race at age 44, Mr Yang was recognised twice by the Obama White House when named Champion of Change and a Presidential Ambassador for Global Entrepreneurship.
What's his platform?
Mr Yang is (almost) a single issue candidate. His first priority will be to implement a universal basic income of $1000 a month for every American adult over 18. He promises to pay for it with a new tax on companies that benefit most from workforce automation, which he says threatens the future of American jobs.
Mr Yang is also in favour of universal healthcare at an affordable price, a shift towards what he defines as "human-centred capitalism", statehood for Puerto Rico and getting rid of the penny.
His campaign before Iowa in one sentence
Mr Yang has proven surprisingly durable, besting a series of high-profile candidates who dropped out as he kept qualifying for debates, but hasn't covered the airtime into a breakout moment in the race.
How will I remember him?
Mr Yang is willing to put his money where his mouth is when it comes to his Universal Basic Income policy.
He gave one person in Iowa $US1,000 a month for a year to demonstrate the benefits of his policy.
The other candidates still in the race
- Tom Steyer — Hedge fund manager and billionaire who entered the campaign late. Has long campaigned on impeaching Donald Trump and on climate change. Has managed to make his way onto more debate stages than many expected
- Deval Patrick — A former governor of Massachusetts and civil rights lawyer. Hoping to appeal to the same moderate voters being courted by Joe Biden
- Michael Bloomberg — Former New York City mayor and the 11th-richest person in the world. A moderate who has pledged to not accept a single donation for his campaign. Mr Bloomberg has managed to register in a series of eye-catching polls thanks to an eye-wateringly expensive advertising campaign. Keep a lookout for a hotly-anticipated anti-Donald Trump ad at the Super Bowl halftime show the day before Iowa
- Tulsi Gabbard — Current Representative for Hawaii, an Iraq War Veteran and former vice chair of the Democratic National Convention (she resigned in 2016 to support Bernie Sanders). Kept true to her reputation of often taking stances more at home in the Republican Party. Has produced a couple of fiery debate performances
- Michael Bennet — A current senator from Colorado who previously served as Superintendent of Denver Public Schools in Colorado. Made some early debates, but has been a non-factor in the campaign
- John Delaney — The former three-term congressman from Maryland chose not to run for re-election during the 2018 midterms so he could focus on his presidential campaign. The first Democratic candidate to announce a run is still hanging in there, but has struggled for support
Candidates who've dropped out
In order by date:
- Richard Ojeda — State senator from West Virginia who lost a highly publicized 2018 US House race. Ran for 10 days on a populist platform of helping the working class
- Eric Swalwell — Representative from California. Ran for 98 days on a gun control platform
- Mike Gravel — Former senator from Alaska and former presidential candidate. Ran for 121 days on an anti-war platform. Said he was never in it to win it, anyway
- John Hickenlooper — Former governor of Colorado. Ran for 165 days as a moderate, pushing pro-business policies. Said he would consider a Senate run
- Jay Inslee — Current Governor of Washington state. Ran for 173 days on a platform of climate change action
- Seth Moulton — Current representative for Massachusetts. Ran on advancing the military, creating public healthcare and passing the Green New Deal. Dropped out after 123 days
- Kirsten Gillibrand — Two-term senator from New York and a former lawyer. Her top priority was supporting women and working families. Ran for 165 days
- Bill DeBlasio — Current Mayor of New York City whose decision to run for President was highly unfavourable among his constituents. Ran for 127 days on a progressive pro-worker, anti-Trump platform
- Tim Ryan — Current representative for Ohio who tried to capture working-class voters in the mid-west. Apart from a minor splash at the opening debates, struggled to have an impact. Ran for 202 days
- Beto O'Rourke — A two-term Congressman from Texas who became a media darling during his unlikely run for the US Senate against Republican Ted Cruz. Dropped out on November 2 after 232 days, prompting Donald Trump to call him a "poor pathetic guy"
- Wayne Messam — Current mayor of Miramar, Florida. Had a platform of fighting climate change and forgiving student loan debt. Ran for 236 days
- Joe Sestak — Former Pennsylvania congressman and retired three-star admiral. Ran on his national security experience and on making healthcare a top priority. Campaigned for 161 days
- Steve Bullock — Current governor of Montana. Running on a moderate platform focused on campaign finance reform. Campaign lasted for 202 days
- Kamala Harris — First-term senator from California with a long resume of legal offices, including as district attorney for San Francisco and attorney-general for California. Had a breakout moment after the first debate, but struggled to capitalise on the momentum. Dropped out after 316 days citing financial difficulties
- Julian Castro — The former mayor of San Antonio, Texas and member of Barack Obama's cabinet made a splash in several debates. But in the end, it wasn't ever enough to lift him into the top tier of contenders. Ran for 355 days but said "that it simply isn't our time".
- Cory Booker — Senator from New Jersey who ran on a platform of positivity, but never really broke through a crowded field. Said he dropped out because of money concerns and the fact that he'd been recalled to Washington to deal with impeachment. Lasted 346 days.
- Marianne Williamson —A 66-year-old spiritual self-help author and activist who wanted to heal the soul of America. Generated a flurry of memes after some memorable debate performances but couldn't make a serious challenge in the 347 days she ran.
