Pete Buttigieg, mayor of South Bend, Indiana, has a narrow lead in Iowa after the Democrats released partial caucus results. Senator Bernie Sanders is in a close second place.
The results come from 71% of precincts from all of Iowa's 99 counties.
It comes after an embarrassing run of events that saw the result of the vote held up for almost 24 hours.
In a call to frustrated campaign representatives earlier on Tuesday, Iowa state party chairman Troy Price said: “We will continue to work through the process."
Miles Coleman, at the UVA Center for Politics, told Euronews that while Iowa was an early caucus with relatively few delegates compared to later primaries, it was "certainly not a good look for the party."
"Most of the blame should fall squarely on the state party, as opposed to the national party," he said.
The delay to the vote comes as a result of reforms to the Iowa caucus that allowed people to vote using an app, which it was later found had a coding error.
Luckily for the Iowa state Democrats, voters were also asked to note down their choice on a sheet of paper, Coleman said, so there will be a paper trail.
Iowa is the first state to vote for party candidates and they do it through what's called a caucus, an important early step in the primary election season.
A caucus is a gathering of voters at a specific time of the day where party members pick their candidate.
The meetings occur in churches, schools, town halls and other local venues and are funded by the political parties.
After the Iowa Caucus, there is a primary election in New Hampshire, a caucus in Nevada and a primary election in South Carolina.
The situation in Iowa may encourage voices that have called for an end to the caucus system, not least because the state is overwhelmingly white and therefore unrepresentative of modern America.
Debbie Wasserman Schultz, the former chairwoman of the Democratic National Committee, told AP on Thursday: “Caucuses are not a fair way to run elections. The party needs to transition to where there are no more caucuses" and focus on “more diverse participation.”