More information is usually for the best, but last night’s NBC/WSJ poll took an unusual step that could detract from our understanding of the horse race. In addition to reporting Obama’s 3 percentage point lead, NBC/WSJ decided to note that Obama leads by 8 percentage points in 12 swing states: the ten true battlegrounds where both sides are investing resources, plus Michigan and New Mexico (rolls eyes). Predictably, political reporters have jumped on this data, implying that Obama holds a structural advantage in the Electoral College. Last night’s poll wouldn’t carry such potency if political observers weren’t still recovering from recent memories of Obama’s supposed springtime advantage in the Electoral College, when Public Policy Polling flooded the zone with evidence of an Obama landslide in every battleground state, giving the president the appearance of a stranglehold on all routes to the White House.
But let there be no mistake: a sub-sample of respondents in a single poll is not a sufficient basis to conclude that anyone holds an advantage in the Electoral College. The swing state sub-sample included a staggering 249 voters, which gives it a margin of error of approximately +/- 6.2 percentage points—probably higher than any full poll conducted this year. One poll should not overwhelm the findings of dozens of state polls conducted over the last two months, which depict an electoral map divided roughly along the same lines as the nation: close, but a slight Obama lead.
RealClearPolitics, Pollster, and FiveThirtyEight all show Obama without 270 electoral votes clearly in his column—and he would easily exceed 270 electoral votes if he held an eight point advantage in the swing states. How big of a deal is an 8 point edge? Obama won the same twelve swing states by 7.6 percentage points in 2008. In the current RCP averages, Obama leads by 8 points in just two of the twelve swing states listed by NBC/WSJ, and if one weights the RCP averages in the 12 NBC/WSJ swing states by state population, Obama leads by approximately 3 percentage points, 47-44. FiveThirtyEight actually gives Romney a better chance of winning the Electoral College while losing the popular vote, in part because many prolific state pollsters have Democratic-leaning house effects.
There is a high evidentiary burden for demonstrating that any candidate holds a structural advantage in the Electoral College. The Electoral College almost always follows the popular vote, and even when the popular vote winner fails to secure the necessary electoral votes, it isn’t necessarily apparent in advance. Heading into Election Night 2000, the fear was Gore winning the Electoral College and Bush winning the popular vote. The exact opposite happened only a few hours later. In an extremely close national election, deviations of only a few percentage points in the closest few states can complicate even the best gamed electoral scenarios.
None of this precludes the possibility that Obama is performing better in the battlegrounds than nationally. There are compelling reasons why Obama could hold a swing state advantage, ranging from his confirmed advantage in 2008 to the relentless campaign against Bain Capital. However, since state polls are published less frequently than national polls, it might take weeks or months before a shift in the swing states shows up in the averages. The NBC/WSJ poll could be a harbinger of such a shift, but alone, it's just not enough to confidently assert that the electoral map tilts Obama’s way.