And then there were two.
The US Democratic primary is staring down the barrel of a prolonged and messy primary campaign, after former Vice-President Joe Biden dominated "Super Tuesday", winning 10 of the 14 states on offer and taking a slight lead ahead of Bernie Sanders in the delegate count.
But what's the wider significance of that to the race? What ARE the Democratic primaries? And why is Super Tuesday so important? On The Detail today TVNZ’s former US correspondent Rebecca Wright breaks it all down for us.
The Democratic Primary determines which of the candidates will stand against Donald Trump in November's national election.
Individual states hold elections where people vote for their preferred candidate.
Each state has a certain number of delegates; the exact number of delegates varies, but is largely based on the states' populations.
These are assigned proportionate to the amount of the vote the candidates receive.
There are 3979 pledged delegates, and a candidate gets nominated by winning 1991 of them.
Super Tuesday is important because it's the closest the primaries get to a nationwide vote: 14 states held their presidential primaries on that day (Wednesday, NZ time), representing about one-third of the total delegates on offer.
The results can send a strong indication who the nominee is likely to be.
This week, Biden seized the momentum from Sanders.
Rebecca Wright has just returned to New Zealand after spending three years in New York as TVNZ's US correspondent.
She says the candidacy battle has wider significance for the future of the Democratic party.
"There is this battle for what it is to BE American … who Americans see themselves to be.
“That is the crux of what’s going on in the US I think. You have this person, Donald Trump, at one end and you have Bernie Sanders at the other end, and that is why politics is so important: there’s a real culture war happening in the United States.
“Bernie Sanders does want a revolution. Many Americans want a revolution too – they’re looking to Bernie Sanders as an outsider, somebody from outside the Washington establishment.
“That’s how president Trump got elected – Bernie is probably hoping that’s how he gets elected too.”
The irony is, Sanders has been a senator for the best part of 40 years, but he is still portrayed as an outsider.
Meanwhile, Wright says Biden’s time as Barack Obama’s vice-president could be a decisive factor in the primary race.
“It’s certainly one of Joe Biden’s strengths: he, at every opportunity, will talk about the Obama/Biden presidency, and that’s certainly part of his attraction.
“He has strong connections to the African-American community through Barack Obama.
“What we haven’t seen so far is President Obama come out and say which way he thinks Democrat voters should swing.
“But I think most Democrats probably know that [he] would be the candidate that Obama favoured.”
But does Wright think either candidate can beat Donald Trump in a presidential election?
Listen to the podcast to find out.