Gallup: Poll of 'likely voters' portends big House gains for Republicans

It’s the biggest guessing game in Washington: How many seats will Republicans gain in Congress this election?

In the latest poll, from Gallup, it doesn’t look good for Democrats.

First, some background: Gallup, like other polling agencies, conducts weekly “generic” polls of registered voters, which ask how likely they are to vote for the Republican or Democratic congressional candidate in their district. The polls are useful gauges of the national mood of the electorate (though not for predicting outcomes of specific races). So far, most generic ballots have been giving Republicans a single-digit advantage – with a few recent polls by other organizations actually favoring Democrats.

But this week, Gallup gave its first estimates for “likely” voters, rather than registered voters – historically a far better predictor of the actual vote. The results are staggering.

While the registered-voter ballot still gives Republicans a slight three-point lead, the Republican advantage jumps – a lot – in the poll of likely voters. Gallup gives estimates for two different likely-voter scenarios – one assuming higher turnout and one lower turnout. If voter turnout is high, Republican candidates have a 13-point advantage. If it's low, they have a whopping 18-point edge over Democrats.

Most voter surveys have shown Republicans to be much more energized about this election, but Gallup's poll shows by far the biggest gap between registered and likely voters to date.

So, what does it mean in terms of numbers?

Historically, Gallup's likely-voter poll correlates closely to the final results for midterm elections in the House. In 1994, when Republicans picked up 54 seats in the House, the last Gallup poll gave Republicans a 7-point lead.

According to this model, by the University of Virginia’s Center for Politics, the current 13-point lead would translate to Republicans picking up at least 71 seats (86 seats, in the low-turnout model). But that is pretty far outside even the most pro-Republican predictions so far.

Also, that model is based on the last Gallup poll before the election, and the race may well tighten significantly in the final weeks of the campaign. According to Gallup’s own analysis, a silver lining for Democrats may be that they have more possibility to build enthusiasm among voters in the remaining month, since Republican enthusiasm levels are already high. “The likely voter model results at this point should be viewed as describing the current state of affairs, but not as predictive of the final party vote shares on Nov. 2,” Gallup analysts write.

Before this poll came out, some models were actually showing Democrats leading in generic ballots – and even, in this recent Newsweek poll, having a gap in their favor when comparing likely and registered voters – leading some experts to wonder if Republicans had peaked too soon.

Polling expert Nate Silver offers an analysis of the data in his blog at The New York Times. When he averaged all the generic polls that have come out since Aug. 1 and that included both registered- and likely-voter results, he found that Republicans have a 2-point lead among registered voters and an 8-point lead among likely voters: a 6-point gap that is still significant, but not nearly as terrifying for Democrats as the gaps in the Gallup poll.

Let the predictions begin.