New York’s 9th Congressional District isn’t the likeliest place for a national political referendum.

Vice President Al Gore won it with 67 percent of the vote in 2000, and Barack Obama carried it by 11 percentage points eight years later. It has been held by a string of high-profile Democrats — including Sen. Chuck Schumer (N.Y.) — for decades.

And yet, the special election set for Tuesday in the Brooklyn and Queens areas between state Assemblyman David Weprin (D) and businessman Bob Turner (R) — a race occasioned by the scandal and subsequent resignation of Rep. Anthony Weiner (D) — is surprisingly close, the result, many observers suggest, of the toxic national political environment and Obama’s low poll ratings.

“Obama wins no popularity contests here,” said Hank Sheinkopf, a Democratic consultant in New York.

In a Siena College poll released late last week, Turner held a six-point edge over Weprin. Obama’s approval rating stood at 43 percent, with 54 percent disapproving.

“Certainly Obama job approval in the 40s as opposed to 50s depresses the Democratic base,” said one Democratic consultant who is monitoring the race, speaking on the condition of anonymity to discuss the election frankly. “And in a small-turnout electorate, this has consequences.”

Republicans — and even some Democrats — are painting the race as an Obama referendum. Ed Koch, a Democratic former mayor of New York, endorsed Turner and likened the impact of his possible victory to that of Republican Scott Brown in 2010 in the special Senate election in Massachusetts. A vote for Turner, Koch said, would “register a protest against the positions of President Obama and the Republican leadership on a number of key issues.”

Even Weprin has been loath to embrace Obama.

“I will probably not refuse to endorse him, because I think I will be more effective by supporting him, but at the same time being very strongly against him on some of his policies,” he told the Jewish Press recently.

Putting all of the blame on the president, however, tells only half (or less) of the story, because the Democrats’ situation wasn’t caused by any one factor.

Although the district is Democratic territory, it is trending toward Republicans. It has a large Orthodox Jewish population that is not thrilled with Obama’s positioning on Israel, as well as large pockets of conservative Catholic voters. (It was the site of the single largest point swing between the 2000 and 2004 presidential elections; after Gore won 67 percent in 2000, Sen. John Kerry of Massachusetts took 56 percent in 2004.)

And Weprin is something (well) short of a star candidate, a sort of last-man-standing pick after many preferred candidates took a pass. New York’s congressional delegation is shrinking by two seats because of slower population growth than the national average over the past decade, and many Empire State political observers expect this district to be eliminated in short order.

Weprin, then, was perhaps the only man who wanted the job. But his lack of campaign skills — he guessed that the national debt was $4 trillion (it’s $14 trillion) and oddly dropped out of a debate at the last minute, citing Hurricane Irene — has created a gaffe-prone image that has further complicated Democrats’ efforts in the district. That he can be linked to the unpopular state capital of Albany — and that he voted in favor of Democratic Gov. Andrew Cuomo’s legislation that legalized same-sex marriage in the state — only compounds the problem.

“It was a perfect storm of horrible,” said one Democratic operative who spoke on the condition of anonymity to candidly sum up the situation.

National Democrats, sensing the momentum hit the party could take if Weprin loses, have rode to the rescue in recent days — spending nearly $500,000 on television ads designed to turn the tide.

But there is genuine skepticism that the race can be saved, and an acknowledgment that a loss would create an even more complicated political environment through which Obama — and his newly announced jobs plan — would have to navigate.

Losing a seat such as this one — despite all of the reasons for such a defeat, outlined above — probably would have a chilling effect on the willingness of Democrats running in vulnerable districts and states to support any aspects of the president’s agenda between now and 2012. And that’s the last thing an embattled White House seeking political allies needs right now.