When it comes to electing the chief executive of the city, New Yorkers are prone to abandon their party preferences. It has been 24 years since voters have selected a Democrat as mayor. This dearth of Democrats has led to something of a municipal renaissance. As recently as the early 1990s, it appeared that New York was doomed to succumb to a wave of crime and a faltering economy.

The last Democrat to win election was David Dinkins, a courtly, affable gentleman whose administration, to most New Yorkers, was stunningly unsuccessful. Elected in 1989 to restore racial peace, Mr. Dinkins saw the opposite: the most tragic race riot the city has every experienced, which occurred in Brooklyn’s Crown Heights, and a boycott of a Korean grocery led by Sonny Carson, now deceased.

Crime was at such uncontrolled levels that parents in some neighborhoods were advised to have their young children sleep in the bathtub, lest they be caught in the crossfire of feuding drug dealers. “No Radio” signs were posted by thousands of New Yorkers in car windows to advise would be thieves that they were simply too late, someone had beaten them to it.

One newspaper pleaded with the mayor to address the crime wave: “Do Something, Dave!”

So in 1993 voters turned to Republican candidate Rudolph Giuliani in 1993, who promised tough tactics. The “broken windows” approach signaled zero tolerance for even the most petty of crimes, which were to be tracked with comprehensive statistical analysis. Even the squeegee men, operating the most petty of shakedowns, were banished.

It worked. The murder rate plummeted to an unimaginable low. Minor crime also diminished, substantially. Budgets were brought under control. The city was turning around. Then voters turned to Michael Bloomberg, a lapsed Democrat who ran first as a Republican, then as an independent. He vowed to carry on Mr. Giuliani’s policies.

But lacking a true crime wave to fight, the mayor turned his attention to building a nanny city. He promoted bicycle lanes (strollers mext?) and tried for controls on the size of sugary soft drinks. The mayor used his fortune to get the City Council to scuttle the term limits that had twice been approved by voter referenda. No wonder New Yorkers tired of Mr. Bloomberg.

Seizing the opportunity to restore their party’s primacy, a number of prominent Democratic officials presented themselves to voters in the primary held last week. All vowed to roll back the anti-crime initiatives, particularly the stop, question, and frisk program the Left bills as an attack on minorities.

The most strident opposition to the city’s public safety initiatives came from candidate Bill DeBlasio, who has served the past four years as the public advocate. Mr. DeBlasio was able to exploit his photogenic bi-racial family and promised a return to “progressive” values, which is shorthand for programs that seek to solve urban problems by raising taxes.

Mr. DeBlasio looks fondly on the Dinkins years. He served under the former mayor, as did his then soon-to-be wife, Chirline McCray. When it appeared that Mr. DeBlasio would have to face a tough run-off of the kind designed to bring candidates to a centrist position, party leaders sought the concession of the number-two, William Thompson, the comptroller. He is a serious and competent man with a track record of achievement, but he caved to the pressure, which notably included efforts by Governor Andrew Cuomo, who up until then had been aloof.

This will turn out to be a momentous mistake. The Democrats now have a candidate who happily occupies the far left of the local political spectrum. This spells opportunity for the Republican candidate Joseph Lhota, a Deputy Mayor under Mr. Giuliani. Mr. Lhota won kudos for his recent stewardship of the Metropolitan Transportation Authority and is well-regarded as a manager. If he prevails in the November general election, it will be because Mr. DeBlasio, in promising change, is seen as unable to protect the real gains of the past 20 years.

The polls are signaling that this scenario, however logical, is unlikely. But count me as not so sure. It will be hard for a man as firm in his “progressive” beliefs as Mr. DeBlasio to move to the center. New Yorkers know that Mr. DeBlasio could well take New York on the road to becoming the next Detroit. So don’t be too surprised if, some time before November, voters start to regret this moment of Democratic unity and start to worry about where it points. It is the Democrats’ dilemma.

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Stop, question, and frisk is how the crime prevention program is known. This cable has been corrected from an earlier edition.