Parrying at the Top, and Lunging Below Rosencrantz and Guildenstern did almost all the talking. The final debate between candidates in the Democratic mayoral primary was supposed to be a dramatic showdown among the surging front-runner, Bill de Blasio, and the two candidates trailing him, Christine C. Quinn, the City Council speaker, and William C. Thompson Jr., a former New York City comptroller. Instead, most of the heat and animation came from the two candidates competing for rock bottom. John C. Liu, the comptroller, was the mad dog, lashing out at the Campaign Finance Board and even, at some points, the panel of reporters. "I still have some time here, all right?" he snarled when told his time was up on an immigration question. Then he squeezed in a few more words, in Spanish, including: "Soy inmigrante!" Former Representative Anthony D. Weiner, who described himself as an "imperfect messenger," nevertheless appointed himself to the role of arbiter of virtue, defending Mr. de Blasio, the city's public advocate, when Ms. Quinn accused him of taking donations from so-called "slum lords," and racing to Mr. Liu's defense when the comptroller argued that the federal investigation into his campaign finances was a plot, as he put it, "to get me out of the race." Tuesday's debate on WNBC was supposed to be the candidates" last chance to challenge their opponents in person. It was the viewers" last chance to gauge the aspirants" mettle and try to pick a winner. Mostly, they got a close-up look at two contenders who are in the distant background in the race. For candidates who lead in the polls, debates, national or local, are more about avoiding mistakes than scoring points, or even scarring the opponent. None of the top three took risks. It wasn't until halfway through the hourlong debate that Mr. de Blasio and Ms. Quinn turned on each other, not blasting each other's proposals so much as finding fault with their records. Ms. Quinn is often described as having a hot temper. Perhaps because the most recent poll suggests that Mr. de Blasio could garner enough votes to avoid a runoff, Ms. Quinn did her best to smile and stay cool, and tried not to identify Mr. de Blasio by name, referring to him as "public advocate," as often as possible. The five didn't disagree on many issues, and that made the debate less a battle than an echo chamber. They all said they favored raises for city employees, none would say by how much, and all used the same explanation, one after the other, saying that it would be wrong to negotiate with the unions in public. For much of the night, Mr. de Blasio and Ms. Quinn followed Mr. Thompson's playbook and stood quietly at their lecterns, a little like high school students at a dance class hoping not to be summoned to demonstrate the tango. Voters didn't get a chance to study the candidates" nonverbal reactions, because the camera always remained fixed on the speaker. It didn't help that some of the questions were fatuous. The very first one asked the candidates to describe what kind of middle-class hardships they themselves had recently suffered. No candidate is foolish enough to complain about his or her own high cost of living; they all admitted that they are doing fine, and most lapsed into campaign boilerplate about the struggles of their parents and grandparents. The candidates were asked how much they earned last year. They all made less than $200,000, except for Mr. Thompson, who said he took in about $700,000 and Mr. Weiner, who said he and his wife earned about $500,000. They were asked the last time they took public transportation, and they all claimed to have done so recently. Everyone except Mr. Liu admitted to having someone come in to clean their homes; Mr. Weiner said that he, too, had a housekeeper, but that as soon as she leaves, he cleans up after her. The debate opened with a kind of highlights reel, with clip after clip of the candidates each saying that they represent the middle class. And that, of course, is the theme of the primary: all the contenders are vying to be the non-Bloomberg, casting themselves as champions of the 99 percent. The debate devolved into an arm-wrestling match over who among the candidates has the most middle-class lifestyle.