A dozen candidates who are seeking the Democratic nomination for president have signed up and paid the filing fee to compete locally for delegates in what will be the Hawaii party’s first-ever mail-in balloting this spring to decide who will win the support of state Democratic Party members.

Wednesday was the deadline for candidates to pay their fees and file to compete locally, and front-runners Vermont U.S. Sen. Bernie Sanders; former Vice President Joe Biden; Massachusetts U.S. Sen. Elizabeth Warren; and former South Bend, Ind., Mayor Pete Buttigieg are all in.

Also filing for the Hawaii contest are Minnesota U.S. Sen. Amy Klobuchar; Hawaii U.S. Rep. Tulsi Gabbard; technology entrepreneur Andrew Yang; hedge fund manager Tom Steyer; former New York City Mayor Michael Bloomberg; Colorado U.S. Sen. Michael Bennett; former Maryland U.S. Rep John Delaney; and former Massachusetts governor Deval Patrick.

California U.S. Sen. Kamala Harris also paid the Hawaii fee and registered, but asked that she not appear on the party ballot because she has withdrawn from the race.

State party officials are estimating that 55,000 or more Hawaii party members will participate in the mail-in and walk-in voting that will wrap up April 4.

That would be considerably more than the 33,716 Democrats who participated in 2016 when Vermont U.S. Sen. Bernie Sanders swept the Hawaii presidential preference voting, easily defeating former Secretary of State Hillary Clinton.

“Mail-in voting will make it easier than ever to participate, and we expect an unprecedented number of voters to return ballots,” said interim Hawaii Democratic Party Chairwoman Kate Stanley in a written statement.

But the Hawaii party, which will run the presidential polling, has almost completely overhauled the voting process since 2016, and there may be quite a bit of confusion surrounding the new system.

Hawaii does not have an open primary system, and voters can only participate in presidential preference voting here if they have both registered to vote and enrolled as members of the state Democratic Party.

Historically that has limited participation in Hawaii’s presidential polling to just a fraction of the people who vote each election cycle for Democratic candidates in state-sponsored primary and general elections. That’s because many of those voters are not enrolled party members.

All of those who do sign up as party members will receive ballots in the mail, and Stanley said there will actually be two rounds of mail-in voting.

Registered voters who enroll with the party by Feb. 18 will receive ballots from a first batch that will be mailed out, and registered voters who sign up with the party after Feb. 18 but before March 8 will receive ballots from a second batch that the party will send out.

People can also register to vote, enroll with the party and vote in person on April 4, Stanley said. The party will open 21 sites across the state that day for people who want to vote in person.

The balloting will be what is called “ranked-choice voting,” with voters asked to pick their three favorite candidates in ranked order.

Each candidate must receive at least 15 percent of the vote in one of Hawaii’s two congressional districts to secure a Hawaii delegate at the Democratic National Convention on July 13 in Milwaukee, Wis. Each ballot will only count once, but ballots where the first choice was a candidate who earned less than 15 percent will then be awarded to the voters’ second choice.

Voters will also be able to vote for “uncommitted.” If the uncommitted choice earns more than 15 percent of the vote, candidates at the state convention in May will run to become an uncommitted delegate to the national convention in July.

In all, Hawaii will send 33 delegates and two alternates to the national convention in July.

The Hawaii Republican Party announced last month it was canceling its presidential preference poll and committing all 19 of its delegates to President Donald Trump because no other GOP candidate filed to compete in Hawaii by the party’s filing deadline.