Anthony Weiner’s surge in the polls from a distant fourth to a likely contender in a run-off with Fernando Ferrer after today’s primary brings to mind another congressman who ran for mayor – Edward Koch – and underscores one of the most misunderstood facts about New York politics: We are not a far-left liberal city.

Primary day highlights the fact that we live in an effectively one-party state, with 5 to 1 Democratic registration advantage. But beneath that facade of political unanimity lies a much more complex picture of an electorate that functions more like a three-party system loosely divided between far-left liberals, urban Republicans, and the moderate, middle-class Koch and Giuliani Democrats who make up the majority of New York voters.

The Democrats’ primary problem is that the closed partisan system of primaries we have here in New York – unusual among most cities in America – empowers the far left of the party often at the expense of the moderate middle class.

In the last two mayoral elections, less than one third of registered Democrats have turned out to vote on primary day. These tend to be the most committed local voters, liberal clubhouse types who follow grassroots politics closely and who often are employed by the city’s bureaucracy itself. With such a comparatively small percentage of the overall electorate determining the general election candidates – and in many cases the winner of the election itself, because there is no functional opposition from other parties in November – the party becomes both stale and less representative of New Yorkers as a whole. This helps explain how broadly popular Republican mayors have led our overwhelmingly Democratic city for the past 12 years.

Mayor Bloomberg was a proud Democrat before he chose to run for office, but he looked at the liberal clubhouse chaos of the local Democratic primary and rationally decided he had a better chance of making his case to general election voters by running as a Republican. Now most polls show that he has more support among local Democrats than any of the candidates running in the Democratic primary.

This broad popularity is not just a function of Mr. Bloomberg’s political style, or the impact of his unprecedented advertising buys. Mayor Giuliani was famously hated by far-left local Democrats, but when he ran for re-election in 1997 polls on the eve of the Democratic primary showed that he had the support of far more registered Democrats than any of the Democratic candidates. In that year’s general election against the president of Manhattan, Ruth Messinger, Mr. Giuliani won the support of 45% of the city’s Democrats, and 4 out of 5 boroughs. He even won in his opponent’s notoriously liberal neighborhood of the Upper West Side, which she had represented in the City Council for the better part of two decades.

Liberal Democrats routinely grow misty-eyed at the memory of their supposed heyday in the 1970s, but the longest serving Democratic mayor of the past four decades, Mr. Koch, distinguished himself by being the most conservative Democrat in the 1977 election.

Mr. Koch was then a congressman representing Greenwich Village, then as now nationally known as a euphemism for liberal. But Koch was relentlessly critical of the excesses of the far-left, proclaiming himself a “liberal with sanity,” as opposed to the “wackos” who served as liberal caricatures with their predictable and frequently hysterical identity politics. Chief among these was Bella Abzug, the far-left icon who was expected to be the Democratic nominee. Koch began the race with 4% name recognition and in sixth place of a crowded primary field. But his outspoken identification with his middle-class roots and blunt, common-sense comments on issues of crime and fiscal responsibility resonated with New Yorkers in the Summer of Sam and the looting of the Blackout. Come the September primary, Abzug’s appeal had faded away, and Mr. Koch victoriously ran against Queens-born Mario Cuomo in the run-off election.

In his new book “Ladies and Gentlemen, the Bronx is Burning,” Jonathan Mahler recalls that at the time, Gloria Steinem darkly opined that the 1977 primary election results “confirmed that the once liberal city had lurched to the right.”

But had our city ever been functionally dominated by the far-left? Outside “happenings” in Washington Square Park and Leonard Bernstein’s dinner parties, even in the 1970s, New York City was still convincingly the home of Norman Lear’s fictional middle class malcontent Archie Bunker.

Now representing portions of Archie Bunker’s home borough of Queens, Congressman Anthony Weiner has been consciously echoing Mr. Koch’s campaign on behalf of the commonsense middle class, calling for tax cuts and standing apart from the rest of the Democratic pack by saying in debates that Mr. Giuliani was a better mayor than Mr. Bloomberg. This may be heresy among Al Sharpton’s inner circle, but these factors helped differentiate Mr. Weiner. Now, like Mr. Koch before him, Mr. Weiner has climbed from single-digit name recognition and the back of the pack to having the big momentum coming into primary day.

Mr. Koch – a Bloomberg backer in this election – happily acknowledged the parallels in an interview with the Sun, saying, “[Weiner] has no major support among the forces that normally win an election, the ethnic constituencies. … He doesn’t have the blacks the Hispanics, or the unions – and neither did I.” “The city is a moderate city,” Mr. Koch concluded, “and that’s what I always was – basically a moderate.”

Heading into this primary day, Democrats might want to consider the lessons of history – centrist Democrats can win citywide elections, but whenever the closed partisan primary nominates a far-left Democrat, moderate Republican reformers hold on to City Hall. That’s an unmistakable message from the electorate about the kind of leadership New Yorkers like – and the far-left liberalism they don’t.