On a warm July evening, as Mayor Eric Adams visited Staten Island to highlight his work on public safety at a town hall meeting, a cross section of some of New York City’s progressive class was nearby, plotting how to make the mayor’s first term his last.

The group had been summoned for a “completely confidential” dinner meeting to discuss how to take on “a dangerous man,” according to an invitation obtained by The New York Times.

The dinner included members of some of the city’s most important left-leaning institutions, including the Working Families Party, and staffers from former Mayor Bill de Blasio’s administration.

There was also a potential challenger they were hoping to recruit: Antonio Reynoso, the 40-year old Dominican American lawmaker who succeeded Mr. Adams as Brooklyn borough president.

As the group dined on a vegetarian menu of homegrown squash Parmesan and beet salad, they strategized over how they might beat the mayor in the 2025 Democratic primary — an unusual pushback to a party incumbent, especially this early in his tenure.

“This is a room full of people who truly believe in the ability to go up against Adams and win,” said Cristina González, one of the hosts, on Thursday, after word of the meeting leaked.

Mr. Adams will likely be a heavy favorite to capture a second term. He remains broadly popular with the coalition of Black and Latino voters outside of Manhattan who sent him to Gracie Mansion. He has already built a campaign war chest that is expected to hit $4.6 million with matching funds, and barring a dramatic reversal, the incumbent mayor would likely enjoy the support of the city’s most powerful labor unions.

Evan Thies, a spokesman for the Adams campaign, said in a statement that the mayor had lowered crime and “invested billions of dollars in working people” and that polls showed he had strong support from New Yorkers.

“The fact that these folks would rather play politics in some back room two years before the election, instead of help the mayor help working people, tells you all you need to know about what they really care about: their own power,” he said.

Liberal and progressive Democrats have made little secret of their dismay over Mr. Adams, a centrist former police captain who ran on a public safety message. They have assailed his moves to cut library funding and universal prekindergarten, his efforts to delay the closing of the Rikers Island jail complex, and his response to the migrant crisis, among other policies.

The dinner was perhaps the clearest sign yet that they are now openly strategizing how best to put forward a formidable challenger.

Ms. González, an alumni of the de Blasio administration who hosted the dinner with her partner Janos Marton, a civil rights advocate who ran for Manhattan district attorney in 2021, at their Staten Island home, described the event as part of a “serious effort” to rally around a progressive candidate who can actually win.

Mr. Reynoso, the only elected official at the dinner, acknowledged that the left was “trying to coalesce early to find one candidate. The strategy is to start early and find one strong candidate this time.”

In an interview, Mr. Reynoso said he was not interested.

“I got elected to be the borough president of Brooklyn,” Mr. Reynoso said. “It’s a big borough, and I have a big job.”

Mr. Adams, the city’s second Black mayor, has made a habit of using the left as a foil, blaming progressives for spikes in crime because they support policies like bail reform and favor reducing the amount of money spent on policing. The mayor has challenged the definition of what it means to be a progressive and often refers to himself as the “original progressive.”

But Mr. Adams has also faced a series of negative headlines in recent weeks and has struggled to respond to the migrant crisis — a situation that has soured his relationship with President Biden and led to people sleeping on the streets in Midtown Manhattan.

“It’s clear that Adams is vulnerable. What remains to be determined is, if there’s a viable candidate to challenge him,” said Rebecca Katz, a liberal operative who has not been part of the anti-Adams discussions, but works with Representative Jamaal Bowman, whose name has been floated as a possible opponent.

Some progressive leaders appear to be coalescing around the idea that the ideal candidate would be a Black or Latino Democrat running to the left of Mr. Adams, but with appeal to a broader ideological range of voters. Even so, that candidate would face a daunting challenge.

Jessica Ramos, a state senator from Queens, has discussed running with people in politics, but has not made a decision, according to a person familiar with the matter.

Zellnor Myrie, a state senator who represents the Brooklyn district Mr. Adams once did, is also said to be in the early stages of considering a run. Mr. Myrie, a lawyer who has made affordable housing a top priority in Albany, declined to comment. But a person familiar with his thinking said he had not moved toward assembling a campaign — despite being pushed by political allies.

Others have tried to convince Mr. Bowman to enter the race. Mr. Bowman, an outspoken former middle school principal, has made no secret of his differences with Mr. Adams over policing and city resources for schools and libraries, but he currently lives in Yonkers in Westchester County and told The Times this spring that he was not interested in running.

Other attendees at the July dinner included Rodrigo Camarena, director of Immigration Advocates Network, and Nisha Agarwal, a former commissioner of the Mayor’s Office of Immigrant Affairs under Mr. de Blasio.

Ms. González, who is Puerto Rican, said it was important that a viable challenger to Mr. Adams be a person of color. The mayor has already said that certain attacks against him were based on his race. He has begun to lean heavily on his base of religious supporters.

“It needs to be a person of color to inoculate them against specific kinds of attacks,” she said. “Those are also the people who are most impacted by his policies right now — it’s important to have someone from the community who is most impacted.”

In the 2021 mayoral primary, the city’s progressives had a disastrous showing. The former city comptroller, Scott Stringer, faced sexual harassment allegations and was abandoned by many of his progressive endorsers. Some on the left supported Dianne Morales, who faced a revolt from her staff. Much of the left finally threw their support behind Maya Wiley, a former top lawyer for Mr. de Blasio; she finished a distant third.

“Whoever challenges this mayor has to be equipped — nothing amateurish,” said Councilwoman Shahana Hanif, a co-chairwoman of the Council’s progressive caucus. “We really need to prop up someone who will unite a broad coalition, understand the progressives and work in collaboration with us.”

Alyssa Cass, a political strategist with Slingshot Strategies who worked on Mr. Yang’s campaign, said the mayor’s opponents should be looking someone with broad ideological appeal.

“Any challenge to Mayor Adams that hopes to be anything other than a pipe dream requires a candidate who can make the case that the functioning of the city is reaching a point of no return — and can make that case with just about every voter who did not support the mayor in 2021,” Ms. Cass said.

Another dinner guest was Bill Neidhardt, a former press secretary for Mr. de Blasio who worked on Brandon Johnson’s winning mayoral campaign in Chicago. He said the discussion focused on “frustrations with the Adams administration,” including his response to wildfire smoke that darkened the skies this summer.

There was “a lot of shared urgency about the moment we’re in right now,” he said, adding: “Also Cristina might be the best chef in all of Staten Island.”