If Republican Bob Turner pulls off an upset in New York’s 9th district special election tonight, you can count on hearing one thing from Obama supporters: excuses. Despite evidence that Democrat David Weprin’s sinking poll numbers are linked to the president’s unpopularity in the district, there are many Obama fans out there who don’t want to hear it. Here are some of the explanations likely to be trotted out if the Democrats lose Anthony Weiner’s old seat:

1. Weprin is a weak candidate:

This one’s already started making the rounds, reports the NY Daily News:

Democratic finger-pointing has already started, with some campaign watchers blaming Queens Democratic Party Chairman Rep. Joseph Crowley for making a poor choice in Weprin.

“They wanted a weak placeholder who wouldn’t pose a problem if the district was eliminated. Well, now Crowley owns the loss if it goes that way,” said one disgruntled Democrat.

He certainly isn’t the strongest, though this didn’t start to become an issue until he started sliding in the polls. Weprin was even met with some praise from left-wing pundits when he entered the race. David Nir at the Daily Kos wrote in July:

Weprin seems like a strong candidate for us, while the Republicans are left with a quartet of second choices. It also seems like, as is often the case, the Conservative Party will serve as the tail that wags the dog: Queens Conservative chair Tom Long said his party will back 2010 candidate Bob Turner. If the GOP doesn’t get behind Turner as well, their already-not-great chances of nabbing this seat will get slimmer.

Even though some Democrats are now grumbling the Queens party chairman should have chosen a more charismatic candidate than Weprin, few would argue Turner is beating him in the charm department.

Both of the contenders have their flaws and their strong points. For example, Weprin’s prominent family and background in politics gave him a head start on name recognition. Then there’s the fact Democrats have tended to do very well in New York special elections recently, even in districts much less liberal-leaning than NY-9.

Public Policy Polling is also skeptical of the blame-Weprin argument. The Democratic polling company actually faults President Obama for the loss, noting that he won 55 percent of the vote in the district in 2008, but his approval rating has sunk to 31 percent.

“If Obama’s approval in the district was even 40 percent, Weprin would almost definitely be headed to Congress,” writes PPP. “He’s getting dragged down by something bigger than himself.”

2. It’s the negative fallout over the Anthony Weiner scandal:

There’s no doubt Anthony Weiner’s popularity has waned in the district. But that alone isn’t enough to explain the trajectory of the NY-9 race. When Weprin and Turner first announced, the Democrat had a comfortable lead in the polls. It wasn’t until late August that Turner started to close in on his opponent. If voters are still punishing the Democrats for Weiner’s scandal, wouldn’t they have been more likely to support Turner back in July, when the controversy was still fresh in everyone’s minds?

Plus, the sexting debacle didn’t seem to be that much of a concern for district voters. Back in June, 56 percent of Weiner’s constituents said they wanted him to remain in office despite the scandal.

3. Demographic changes:

One of the more compelling arguments is the demographics in NY-9 have shifted far to the right during the past few years due to population changes. But PPP found the current voter breakdown in its latest poll matches up with 2008:

One final note on the poll and what perhaps should concern Democrats most of all. 55 percent of voters in the district report having voted for Obama in 2008, which is the actual percentage of the vote he got in the district.  Last year, a lot of the races Democrats lost were because their voters didn’t show up and the electorate was far more conservative than for a presidential year.  When you lose that way you can say, well, our voters will come back out in 2012 and we’ll be fine.  But there is no enthusiasm gap here.  Obama voters are showing up in the same numbers they did in 2008.  But only 65 percent of them are voting Democratic.  That’s a really big cause for concern.

Along these lines, voters in the district are still largely supportive of state Democratic politicians. Andrew Cuomo and Chuck Schumer both get high marks in the polls. So the issue isn’t that NY-9 voters are opposed to Democratic policies in general. They’re just not fans of Obama.