Despite the enthusiasm generated by the Democratic National Convention, there remains evidence that a slightly large gap between registered and likely voters continues to persist.

On average, likely voters surveys conducted since the conclusion of the DNC show Obama leading by 3.3 points compared to registered voter surveys showing Obama ahead by 6.3 points. Similarly, polls detailing results for both registered and likely voters show Obama outperforming among likely voters by 3.2 points. 

However, a closer look suggests that the gap is somewhat smaller than the roughly 3-point gap suggested by the simple averages listed above. Langer Research conducted the Yahoo/Esquire and ABC/Washington Post surveys, and both show a large gap between registered and likely voters. If the two Langer Research polls are averaged and treated as one, the gap between registered and likely voters falls to a more typical 2.1 points. Similarly, Rasmussen weighs down the likely voter average without a commensurate influence on the average of registered voters. If they’re excluded from the likely voter column, Obama leads by 4.1 points among likely voters, compared to 6.3 points among registered voters--again producing a more typical gap. And if one only compares polls with LV and RV tallies before and after the conventions (Fox, CNN, ABC/Post), the gap falls from 3.6 points pre-convention in those three surveys to 2 points after the conventions. All things considered, it appears that the gap between registered and likely voters polls diminished marginally over the last few weeks--perhaps by half a point, maybe more. But there are so few polls that the next survey could easily show a big RV/LV gap and send this number back in Romney's direction, as CBS/NYT did this morning. And the early polls have shown conflicting signals, with a growing RV/LV gap in the Washington Post poll and a diminishing gap in CNN and Fox News.

Certainly, Obama has been aided by more Democrats claiming to be enthusiastic about voting this November. But Democrats remain less likely than Republicans to indicate that they’re “certain” to vote, and this difference seems partially responsible for the divergence between polls like CNN and Fox, which seem to rely on enthusiasm and interest to determine their likely voter screens, and the Langer Research surveys which include the self-reported intentions of the voters themselves. This pattern was first observed by Mark Blumenthal, and a report by the Washington Post provided additional evidence. Just 69 percent of the voters who are “somewhat” or less enthusiastic about voting their support for Obama say they are absolutely certain they will vote this fall, compared to 93 percent of “very enthusiastic” Obama voters. The 24 point gap between the self-reported voting intentions of “very” and “somewhat” enthusiastic Obama supporters is more than twice as large as it was at this time four years ago.

By moving more voters into the “very enthusiastic” column, the DNC helped the president. If the debates and rallies of the next few months can move even more Democrats into the “very enthusiastic” column, as they probably will, then Obama might close the gap a little more. But the biggest challenge for the Obama campaign is convincing the remaining “somewhat enthusiastic” Obama voters to turnout and vote. This is probably where Obama’s expansive ground operation needs to make a difference, and it’s also a potential reason why Obama might do better in battleground states, where higher stakes might drive higher turnout among less enthusiastic Obama supporters.