Thompson and de Blasio Vie for Opening as Quinn Rises William C. Thompson Jr. stood in front of City Hall on Monday flanked by two elected officials, both of them pastors. One by one, each called for New York State to stop prosecuting nonviolent 16- and 17-year-olds as adults. Two miles uptown, Bill de Blasio accepted the endorsement of a tenants" advocacy group. Outside the Stuyvesant Town apartment complex, he vowed to go to Albany and lobby for the repeal of a law that effectively took control of rent regulation out of the city's hands. Amid mounting calls for Anthony D. Weiner to drop out of the race for mayor over his lewd online exchanges with women, Mr. Thompson and Mr. de Blasio are trying to seize an opening: to be the alternative to Christine C. Quinn, the City Council speaker, who is once again seen as the front-runner for the Democratic nomination. A new poll released by Quinnipiac University on Monday suggested that as Mr. Weiner's standing had been eroded by scandal, Mr. Thompson, a former city comptroller, and Mr. de Blasio, the public advocate, had leapt past him and were now neck-and-neck behind Ms. Quinn. The primary will be held on Sept. 10, and a runoff will follow on Oct. 1 if no candidate receives 40 percent or more of the vote. The poll, which was conducted from last Wednesday to Sunday, found Ms. Quinn with the support of 27 percent of likely Democratic voters. She was followed by Mr. de Blasio with 21 percent, Mr. Thompson with 20 percent and Mr. Weiner with 16 percent. The poll had a margin of sampling error of plus or minus five percentage points. On Monday, in the midday heat, Mr. Thompson and Mr. de Blasio held bread-and-butter campaign events aimed at important bases of support - for Mr. Thompson, minority voters, and for Mr. de Blasio, middle-class liberals. Mr. Thompson's appearance came a day after he delivered a forceful speech in which he criticized the New York Police Department's stop-and-frisk policy, asserting that the city's policing tactics were rooted in the same racial stereotyping that had led George Zimmerman to confront Trayvon Martin in Florida. Mr. Thompson was flanked by Councilman Fernando Cabrera, a Bronx Democrat, and Assemblyman Karim Camara, a Brooklyn Democrat who is the pastor of the church at which Mr. Thompson delivered his head-turning speech on Sunday. "Today I feel compelled to speak in the same vein, because the rules of our criminal justice system are failing young people and families, especially in our communities of color," Mr. Thompson said before lamenting that New York and North Carolina are the only states that treat 16-year-old defendants as adults. Around the same time, Mr. de Blasio received the endorsement of Tenants PAC, a group that works to elect candidates who will fight rent increases and preserve the supply of rent-stabilized and rent-controlled housing. Standing on the corner of 16th Street and First Avenue, Mr. de Blasio said that under his mayoralty, every major development would be required to have affordable housing on or near the site. "Last time I checked, it wasn't the real estate industry's town, and we were just living in it," Mr. de Blasio said, in remarks punctuated by applause and shouts of "That's right!" from the two dozen tenants gathered, who were holding "De Blasio for Mayor" signs. Earlier in the day, Mr. de Blasio had been in Brooklyn, where he put forth a plan to coordinate spending among small Brooklyn hospitals, in order to save the financially troubled Long Island College Hospital, which has been scheduled to close. At the tenants" event, he brought up that fight to take a veiled dig at Ms. Quinn, whom some downtown residents accuse of not doing enough to save St. Vincent's Hospital Manhattan in Greenwich Village. The hospital closed in 2010. "We lost health care, we got condos," he said. That's not the future of this city. In an interview later on Monday, Mr. de Blasio said that he believed the race was now wide open. "People are just beginning to focus," he said. It's anybody guess right now which combination of candidates will be in the runoff. Mr. Weiner, campaigning in Queens, dismissed calls from prominent Democrats and newspaper editorial boards that he drop out of the race. "I am going to leave this decision to the people of the city of New York, period - end of conversation," Mr. Weiner, a former congressman, told reporters outside a senior center. It's their decision. It's not yours. It's not mine. It's not some Sunday talk show pundit's. With his campaign in critical condition, Mr. Weiner affirmed his outsider status in a fund-raising letter to supporters on Monday, with the subject line, "I'll let you decide." "A lot of people who don't have a vote want to decide who our next mayor will be," Mr. Weiner wrote. They've all made up their minds that they want to stop our campaign right now. But the Quinnipiac Poll suggested that likely Democratic voters had also soured on his candidacy: 53 percent said he should drop out of the race. Gov. Andrew M. Cuomo, a Democrat who has stayed out of the mayoral race, said on Monday that he would not join the chorus of Democrats asking Mr. Weiner to drop out. He said it was not his place to say who should or should not run for office. But when asked about Mr. Weiner's candidacy, Mr. Cuomo was not encouraging. "This is summer political theater in New York," he told reporters on Long Island. We laugh, because if we didn't laugh, we would cry. Javier C. Hernández and Kate Taylor contributed reporting.