I used the same polling-snapshot method as in past years: I calculated a compound probability distribution of all contested races. The graph shows a history, over time, of the probability of Democrats/Independents getting 50 or more votes in an election based on today’s opinion polls. On Election Eve, opinion polls closely track final outcomes. Therefore, consider this a snapshot of Campaign 2014.
A few weeks ago, I wrote about different kinds of Senate models: Type 1 models based on fundamentals, vs. Type 2 models based purely on polls. The graph above is a snapshot of polls, and is pure Type 2. Can it be turned into a prediction? Yes, although this year will be especially difficult because it’s such a tight race – as close as the Kerry v. Bush presidential race in 2004, or Gore v. Bush in 2000.
Why is prediction hard? Because the probability of Democratic control is highly sensitive to swings in national opinion. The change you see above, from 90% in April to 52% today, could be reversed by a tiny swing in national opinion. Right now, six Senate races are close to dead heats: Alaska, Colorado, Georgia, Iowa, Kentucky, and Louisiana. If the Democratic-vs-Republican margin in these races swung by two points in either direction across the board, the probability of a takeover by would go to 90% in either party’s favor.
Where will things go by November? As far as I can tell, three factors are going to matter. Two of them I’ve written about before:
1. Consolidation of GOP support behind their nominee. We’re waiting for GOP primaries in Georgia (July 22) and Alaska (August 19). In addition, Louisiana has a peculiar system in which many candidates appear on the November ballot, with a possible runoff in December. In each case, once Republicans settle on a single nominee, he will start to consolidate support. But by how much?
2. President Obama’s approval rating. In the graph above, do you see that precipitous drop in May? It corresponds to a subtle shift in the President’s approve/disapprove numbers. The similarity is only visible with aggregation:
Swings like this occurred in 2012, when the Senate and Presidency seemed to move together. I’ll analyze the possible relationship between Presidential approval and Senate races in coming weeks.
Finally, we have one factor that really limits the Meta-Analysis for now: an absence of data.
3. Alaska, Alaska, Alaska. The biggest problem with the polling snapshot right now is a near absence of information about the Alaska race. Senator Begich (D) is locked in a close race with the probable (but not definite) nominee, Dan Sullivan (R).In other close states, there’s at least a little June data. The last published Alaska poll that went into today’s snapshot was completed on May 11th (see HuffPost), before Sullivan made a possibly-significant gaffe, accusing Begich of not bringing home pork-barrel spending – in an advertisement shot on top of a building that Begich got built.
Sullivan is also fighting off fellow Republican Mead Treadwell in the primaries. On the general election ballot, Begich and the eventual GOP nominee may also face competition from Libertarian and Alaska Independence Party nominees, who would probably draw net support away from the Republican nominee.
Normally I don’t pay attention to single polls. But for the reasons I’ve given, I was super-interested in this survey by Ivan Moore. Depending on what it says, it would move the overall Senate-control probability by as much as 10% in either direction. However, I note that even this data point would be hard to interpret. Alaska is hard to poll because of its physical size and rural and indigenous populations.
Other polling nerds like to complain about the absence of good polling data. Alaska is the place where a single well-done survey could give the most information.