Both Hillary Ronen and Joshua Arce officially announced their candidacies for District 9 supervisor this week, joining Edwin Lindo in the race for the Mission, Bernal Heights, and Portola seat.

Ronen, who has served as chief of staff for Supervisor David Campos since 2010, said she would hold an official announcement event Thursday at 4 p.m. outside of St. Luke’s Hospital. Five of the six progressive supervisors — Campos, Jane Kim, Aaron Peskin, John Avalos, and Eric Mar — plan to attend, joining former state assemblymember Tom Ammiano in endorsing Ronen.

Arce quietly filed paperwork Wednesday evening declaring his intent to run before speaking to a few dozen supporters at Bissap Baobab, including Lou Fischer, recently-elected head of the Alice B. Toklas LGBT Democratic Club, and Larry Del Carlo, former Mission Housing president.

Lindo held a campaign kick-off back in December and has been fundraising and canvassing since, spending his weekends meeting and greeting residents of the district. Lindo was also a vocal advocate of the Mission moratorium and is a fixture of the protest movement against police shootings.

Ronen said Wednesday she is committed to seeing 5,000 new affordable housing units built in the district in the next 10 years.

“We are living in the worst affordability crisis of the city’s history,” said Ronen. “It’s a totally achievable goal. It’s not going to be easy, it’s going to take everybody working together, but then we can have the San Francisco that we grew up in and moved to.”

Ronen said she would look to develop empty and underutilized sites and raise heights “where appropriate” to build the units, and would seek funding from another housing bond, the state and federal government, and the city budget itself. She also took aim at Mayor Ed Lee’s administration, criticizing it for “constantly leaving money on the table” from corporations that should “contribute to solving the housing crisis.”

“I am going to be laser-focused on building these units,” she said. “If you have someone who is focused on building the housing that we need, and using all the tools to get there, it can happen, and we can make it happen.”

Arce also pledged to build “thousands and thousands” of housing units and pointed to his experience with labor unions and as board member of the non-profit developer Mission Housing, saying he had a plan that would “really move the needle on affordable housing.”

He was thin on specifics and endorsements, promising further details during a formal announcement event in February.

Lindo, too, listed housing as a central issue, but said crafting a “self-determined” district focused on “equity, social justice, and unity” was a centerpiece of his campaign. The 29-year-old was born at St. Luke’s, fought an eviction with his undocumented Nicaraguan father for 10 years, and remembers “having to use every available public resource to survive.”

“The difference is that the policy that I would be creating is through the lens of my lived experience,” he said, adding that his four months as an intern for Supervisor Campos — where he worked under Ronen — gave him the required experience.

A relative newcomer to political scene as well as Mission native, Lindo is the most home-grown candidate but does not have the weighty endorsements of his opponents. Five of the six progressive supervisors are backing Ronen, who, with Ammiano’s and Campos’s endorsements, keeps alive a tradition in District 9 of incumbent supervisors mentoring their replacements.

“What I’ve seen is someone who understands how city hall works, who knows what it takes to be effective, and who has a very thorough grasp of the issues,” said Campos, underscoring Ronen’s involvement in all the legislation he has passed in the last five years.

Arce, on the other hand, may have heavy donors and the local Democratic machinery on his side. Labor unions are traditional allies of building developers — big spenders in city elections — and alongside his candidacy for supervisor Arce is running for re-election to the Democratic County Central Committee in June.

The 2016 supervisorial elections are critical for the balance of power on the Board of Supervisors. With three of the most left-leaning supervisors — Campos, Mar, and Avalos — termed out and Peskin, London Breed, and Norman Yee up for re-election, moderates need just two wins to regain the 6-5 majority they held before the progressive victory last November.

The State Senate race between progressive Kim and moderate Scott Weiner also throws a wrench into predictions of the post-election landscape. A recently devised charter amendment may ensure an election for the seat left open by whoever departs for Sacramento. But if the ballot measure fails, Mayor Lee will be able to appoint a supervisor for either District 6 or District 8 until 2018.

Correction: An earlier version of this article stated that Edwin Lindo was an intern for Supervisor David Campos for “years.” He was an intern for four months, and the article has been updated.