[Updated Thursday 7 p.m. EDT] The surprising ascendancy of New York City Public Advocate Bill de Blasio may have energized the liberal wing of city Democrats, but the commanding mayoral front-runner has some Republicans cheering as well.

Despite the fact that the Republican line has won the mayor’s office five consecutive times in New York, conventional wisdom has long had the Democratic nominee easily winning the Nov. 5 general election this year.

It is still a city in which registered Democrats outnumber Republicans 6 to 1, after all, and which gave Obama 81 percent of its votes in 2012. Even the Democrat-turned-Republican-turned-Independent Mayor Michael Bloomberg, who won three terms on the Republican line, has deftly played down standard partisan divisions during his 12-year tenure.

But Mr. de Blasio has stunned the more moderate Democratic candidates the past few weeks with his relentless critique of the Bloomberg administration, as well as his dogged liberal message of income inequality in the shadow of Wall Street wealth. He also was very effective showcasing his interracial family – including his teenage son, Dante, whose Afro-style hair and descriptions of his father in campaign commercials have become some of the most memorable of the race.

With the support of 43 percent of likely Democratic voters, he could win the primary without a runoff, according to the latest Quinnipiac poll.

Yet these same traits, so appealing to a growing segment of city Democrats, could be used against him come November.

“Republicans will be looking to really frame this election as continuing the course, going forward with the progress we’ve made as a city under [former Mayor Rudolph] Giuliani and Bloomberg," says David Johnson, a senior Republican consultant and CEO of Strategic Vision, an Atlanta-based political consulting agency. "And they see [de Blasio’s rise] as a chance to really frame it this way.”

It’s an argument that Republicans would have much more difficulty launching against the other top Democrats, including City Council Speaker Christine Quinn, or former Comptroller Bill Thompson, both of whom who have run careful, centrist campaigns – at least by New York City standards.

“With Quinn, and with some of the others like Thompson, Republicans don’t see this dynamic as much,” continues Mr. Johnson, a veteran of high-profile political campaigns. “But de Blasio, they do, and they feel really that they have a chance to hit him for being so liberal, so out of step and potentially costly to New York.”

Make no mistake, the odds are still stacked against either of the leading Republican candidates. Joe Lhota, former deputy mayor under Mayor Giuliani, currently leads John Catsimatidis, the billionaire owner of a grocery store chain, by a 2-to-1 margin, according to the Quinnipiac poll.

But Republicans could see a glimmer of hope against a de Blasio nomination, many observers say.

“They’ll essentially do what Christine Quinn and Bill Thompson are doing, because they are also more to the right of Bill de Blasio,” says Christina Greer, a professor of urban politics at Fordham University in New York. “And that is framing him as this pie-in-the-sky progressive liberal who has great ideas, but that they’ll never get past Albany, and that he’ll never have the money or the cohesion to accomplish anything.”

Indeed, with his call for increased taxes on incomes over $500,000 to fund universal pre-K programs and middle school after-school programs, New Yorkers haven’t seen a major candidate with such a progressive platform since Democrat David Dinkins – a fact Republicans will seek to exploit.

“They’ll try to paint him as somebody who wants to redistribute wealth and income,” says David Mark, editor-in-chief of the online political site "Politix." “And they’re going to try to appeal not just to the wealthy, but also the middle-class people who are struggling just to get by and have some kind of decent life style in New York City, and really paint him as a socialist redistributionist.”

“So, he might be easier to demonize, when he talks about income equality,” continues Mr. Mark. “In some ways, he comes off sounding fairly radical, but I still think there’s still enough mainstream Democrats in the city who are likely to support that point of view.”

But even de Blasio’s multicultural and nontraditional family could cause some problems in the general election – even in a city like New York. His wife, Chirlane McCray, was a high-profile lesbian activist who wrote a groundbreaking article for Essence magazine in 1979, describing her coming out as a gay black woman.

According to GOP consultant Johnson, who says he is familiar with some of the internal polling of the Lhota campaign, there are a number of groups, including many Jewish voters, who remain uncomfortable with de Blasio.

“Despite all the popularity, despite everything we’ve heard about his son stealing the show, they’re also seeing, too, that there is still some backlash about the mixed marriage,” he says.

[Editor's note: The following two paragraphs have been added after initial publication, for further clarification.

The Lhota campaign says there is no truth in Johnson's statement, and expressed outrage on Thursday that the Monitor did not seek to confirm it before publishing such an assertion. "I can say with 100 percent certainty that this question was never polled by our campaign, and this guy has never seen any of our polls," said spokeswoman Jessica Proud, who contacted the Monitor on Thursday after Johnson's claim about internal campaign polling drew attention in the press. "I don’t even know who he is. No one on our campaign knows who he is.”

In three separate followup conversations with the Monitor on Thursday, Johnson affirmed that he was quoted accurately and in the correct context. He did, however, say that he "misspoke" about his sources inside the Lhota campaign and that he had meant to say he "wouldn't be surprised" if there were internal polling about attitudes toward de Blasio's multicultural marriage.]

But before anyone crowns the current public advocate as the Democratic nominee, observers point out that a one-on-one showdown in a runoff with either Quinn or Thompson could be a lot closer than polls currently show. A majority of Democrats could end up thwarting Republican hopes to run against such an unabashed liberal.

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“Suppose there is a runoff,” says Ms. Greer. “We’re asking people to come out Sept. 10, Oct. 1, and Nov. 5. That’s a lot.... A primary like this would benefit someone like Thompson, who’s part of the old guard: He’s got the United Federation of Teachers, and they are highly, highly organized. But he’s also got older people of color – the people who actually turn out to vote in primaries.”

“We’re asking Democrats to possibly vote three times in two months,” she says. “So, polls are great, but it’s all about turnout.”