Both are possible. My presumption is to defer to the balance of pollsters, so I wouldn't discount the polls if they collectively pointed toward a whiter electorate, much in the same way that it's a mistake to ignore the Democrats' persistent edge in party-ID. It's also important to make comparisons within polls, rather than with the exit polls. As a general rule, surveys have shown whites as a larger share of the electorate than the exit polls, which differ over simple but potentially important wording issues. For instance, the exit polls ask voters if they are "Latino," other telephone polls ask if people are "Hispanic," and other still don't provide the option of "Hispanic" or "Latino," but then ask a follow up about whether they consider themselves Hispanic or Latino after categorizing them within more standard racial categories. The multi-cycle consistency of demographic house effects provides added cause to focus on comparisons within polling firms.

Unfortunately, there aren't many post-debate national polls with racial/ethnic breakdowns for 2012, 2010, and 2008. But those that do seem to suggest an electorate more reminiscent of 2008 than 2010. The most recent Battleground/Lake/Tarrance poll showed whites as 79 percent of the electorate in 2008, 78 percent in 2010, and 77 percent in 2012. The NBC/WSJ poll showed whites as 76 percent of the electorate in 2008, 78 percent in 2010, but 74 percent in their most recent survey. And although Monmouth/SurveyUSA doesn't have a corresponding poll for 2008, they show whites as just 72 percent of the electorate. PPP's recent tracking poll puts whites at 71 percent of the electorate. On the other hand, the ABC/Washington Post poll seems to be whiter than it was in 2008, although an exact number can't be calculated because they now provide a single result for non-white voters, even though they disaggregated African Americans and Hispanics in 2008.

This probably doesn't represent enough data to assert that there is a "consensus" that the electorate will be as diverse as it was four years ago, so it's not clear that Gallup is off on a limb. But if more data depicts such a consensus with Gallup's standing alone, then this might go some way towards explaining how Obama holds such a large lead in their poll of likely voters. If Gallup showed whites as 77 percent of the electorate instead of 80 percent, Obama would gain a net-3.7 points among likely voters (based on their internals from earlier this week).

It's important to remember that Gallup appears to weight its sample of adults to census targets, which suggests that major differences in changes in the racial composition of the electorate should be the result of their likely voter screen, not the composition of registered voters (although this is not assured). Likely voter screens are much more of an art than a science and they're calibrated to predict the behavior of the electorate on Election Day. That makes them potentially less useful a few weeks out, when many voters might not yet be paying full attention, haven't researched where they'll vote, and before the effects of GOTV efforts. Gallup has a long history of showing big swings in its likely voter model and Gallup showed a large gap between likely and registered voters that eventually closed by Election Day in 2008. Something similar could occur again.