NEW YORK (AP) — Thirteen Democrats and two Republicans engaged in a last effort to rally supporters Tuesday as voters cast their ballots in New York City's mayoral primary, the first citywide election to use ranked choice voting.

Several candidates in the race to succeed Mayor Bill de Blasio have the potential to make history if elected. The city could get its first female mayor, its first Asian American mayor or its second Black mayor, depending on who comes out on top.

But with the debut of the ranked voting system and a mountain of absentee ballots still at least a week away from being counted, it could be July before a winner emerges in the Democratic contest.

Brooklyn Borough President Eric Adams, a former police captain who co-founded a leadership group for Black officers, has led in several recent polls. But he’s been closely trailed by former city sanitation commissioner Kathryn Garcia and former de Blasio administration lawyer Maya Wiley, with former presidential candidate Andrew Yang also in pursuit.

“This has been an amazing journey,” Adams told reporters after voting in Brooklyn, emotionally recounting how his path into both law enforcement and politics began at age 15, when he was beaten by police officers. “A little boy, laying on the floor of the 103rd Precinct, assaulted by cops, now could become the mayor to be in charge of that same police department.”

After polls close at 9 p.m., New York City’s Board of Elections plans to release partial results of votes cast in person, but that initial picture could be misleading because it will only include data on who candidates ranked as their first choice.

The ranked choice system, approved for use in New York City primaries and special elections by referendum in 2019, lets voters rank up to five candidates on their ballot.

Vote tabulation is then done in computerized rounds, with the person in last place getting eliminated each round, and ballots cast for that person getting redistributed to the surviving candidates based on voter rankings. That process continues until only two candidates are left. The one with the most votes wins.

It won’t be until June 29 that the Board of Elections performs a tally of those votes using the new system. It won’t include any absentee ballots in its analysis until July 6, making any count before then potentially unreliable.

More than 87,000 absentee ballots had been received by the city as of Monday, with more expected to arrive in the mail over the next few days.

Besides Adams, Garcia, Wiley and Yang, other contenders in the Democratic contest include City Comptroller Scott Stringer, former U.S. Secretary of Housing and Urban Development Shaun Donovan, former Citigroup executive Ray McGuire and nonprofit executive Dianne Morales.

De Blasio, a Democrat, leaves office at the end of the year due to term limits.

In the Republican primary, Guardian Angels founder Curtis Sliwa faced off against businessman Fernando Mateo. Because there are only two candidates in that race, ranked choice voting won’t be a factor.

The candidates raced around the city Tuesday doing a last round of campaigning.

Wiley was losing her voice greeting voters near her polling place in Brooklyn. Garcia campaigned up in the Bronx, while Sliwa and Stringer bumped into each other campaigning in Manhattan.

Yang rode the subways to meet voters.

“If you want your city to work for us and our families, you have got to get out and vote,” he said after voting in Manhattan.

Concern over a rise in shootings during the pandemic has dominated the mayoral campaign in recent months, even as the candidates have wrestled with demands from the left for more police reform.

As a former officer, but one who spent his career fighting racism within the department, Adams may have benefited most from the policing debate.

He denounced the “defund the police” slogan and proposed reinstating a disbanded plainclothes unit to focus on getting illegal guns off the streets.

Wiley and Stringer, battling for progressive votes, both said they would reallocate a portion of the police department’s budget to other city programs.

Of the top contenders, either Garcia or Wiley would be city’s first female mayor if elected. Adams or Wiley would be the second Black mayor. Yang would be the city’s first Asian American mayor.

Yang and Garcia formed an alliance in the campaign’s last days in an apparent effort to use the ranked voting system to block Adams. The two held several joint campaign events, with Yang asking his supporters to rank Garcia as their No. 2 — though Garcia did not quite return the favor, not telling her voters where to rank Yang. Adams accused his two rivals of purposely trying to block a Black candidate.

Neither Sliwa nor Mateo has much of a chance to win the November general election in a city where registered Democrats outnumber Republicans by 7 to 1.

Former allies, the two Republicans traded personal insults and tried to shout over each other during one debate on Zoom.

Sliwa, a radio host who still wears his red Guardian Angels beret when he appears in public, got an endorsement from former Mayor Rudy Giuliani, who called him “my great friend” in a robocall to Republican voters.

Mateo, a restaurateur who has led organizations advocating for car service drivers and bodega owners, was endorsed by Michael Flynn, former president Donald Trump’s first national security adviser.