In the latest wave of the New York Times/CBS/YouGov poll, Cory Booker leads Jeff Bell 51-39.
Bell's admirers (of which I'm one) might be tempted to conclude: Not a bad showing for Bell in a race where the conventional wisdom has been that Booker would win by at least 20 points. Bell's run an interesting campaign, he's raised important issues, it looks as if he'll achieve a respectable if losing result while being massively outspent, and one can leave it at that.
Not quite so fast.
Take a look at some of the poll's internals. Booker is winning Democrats by 91 to 4 percent; Bell is winning Republicans by the exact same overwhelming margin. Those numbers were predictable. (Polarization, anyone?) But take a look at this: Bell is winning independents, who are expected to be close to a third of the electorate, by 45 to 37 percent. I'm not sure observers would have predicted that.
So if Bell is leading among independents, why is Booker ahead? Well, because there will be more Democrats than Republicans voting on Election Day in New Jersey. How many more? That's the question.
The Democratic registration edge is about 7 to 4, and YouGov seems to have weighted the sample accordingly. But what if Democratic turnout is down (Obama has about a 41 percent approval in New Jersey)? And what if Republican turnout is up? If the partisan differential gets smaller, at some point Bell's lead among independents can make up the gap.
To their credit, YouGov releases the unweighted as well as the weighted results from its poll. As it happens, YouGov's unweighted sample, for whatever reason, has about a 6 to 5 ratio of Democrats and Republicans. With that kind of less dominant partisan breakdown, and with his lead among independents, Bell pulls into something close to a dead heat with Booker.
Of course the fact that the poll happens to have a 6 to 5 partisan distribution doesn't suggest that will be the distribution on Election Day. But it does show how much Booker's lead depends on Democrats coming out to vote in traditional numbers, and also on no further erosion of what is already a surprisingly weak showing by Booker among independents. Neither of those is assured.
This race may not be over yet.