De Blasio Could Avoid Democratic Runoff, New Poll Suggests Bill de Blasio, the front-runner in the Democratic primary for mayor, has surged to a commanding lead that, should it hold, could allow him to accomplish what once seemed unthinkable: become the party's nominee without a runoff. A new survey from Quinnipiac University finds that 43 percent of likely Democratic voters plan to support Mr. de Blasio, the New York City public advocate, in the primary next Tuesday. William C. Thompson Jr., who captured the Democratic nomination in 2009 but lost the general election that year to Mayor Michael R. Bloomberg, was supported by 20 percent of likely Democratic voters. Christine C. Quinn, the City Council speaker, who had been the front-runner for most of the campaign, now has the support of 18 percent. The 43 percent for Mr. de Blasio is by far his best performance in a public poll during the campaign. A runoff will be held, on Oct. 1, only if none of the nine Democrats on the ballot receive 40 percent of the vote. The poll, released just hours before the final televised debate in the Democratic primary, is likely to intensify pressure on Mr. Thompson and Ms. Quinn to use the high-profile forum to alter the dynamic of the race. Mr. de Blasio has staked his campaign on being the most liberal of the top contenders, and offering the cleanest break from Mr. Bloomberg, a political independent. He has vowed to raise taxes on the wealthy to finance early childhood education, has railed against the Police Department's stop-and-frisk practice and has even been arrested while protesting the potential closing of a Brooklyn hospital. He has also made television advertisements featuring his interracial family that have been some of the most memorable commercials this year. Whether Mr. de Blasio will actually retain his lead, much less avoid a runoff, remains to be seen. The Thompson campaign, in particular, has argued that private polling indicates a far tighter race among the top three contenders. Moreover, many New Yorkers have historically waited until the last minute to make up their minds. Conventional wisdom suggests that a number of people are just beginning to tune in to the election, as they transition out of summer and gear up for the start of the school year next week. In one sign of how fluid the race remains, 24 percent of those surveyed by Quinnipiac said there was a "good chance" that they would change their minds in the next seven days. The new poll has a margin of sampling error of plus or minus four percentage points. Quinnipiac University surveyed 750 likely Democratic voters between Aug. 28 and Sept.