Using the technique outlined in my first Senate piece, I estimated what the president’s job approval would be in these states for each incremental increase in national job approval from 38 to 55 percent.
Finally, for each job approval rating increment, I ran 20,000 simulations for each race. The president’s estimated approval is used as the midpoint, and almost all of the simulations are kept within 10 points of that midpoint (two reasons: 1) no Democrat in a competitive race, with the possible exception of Joe Manchin in 2010, has run more than 10 points ahead or behind the president’s job approval in their state; 2) if you run the regression of job approval vs. outcomes, the standard deviation is five).
You can click here to see how often an average Democrat would be expected to lose each individual race to an average Republican at each job approval interval.
The next step is to total up our simulations, showing how frequently Republicans would win the Senate at each job approval interval for Obama.
This is a grim picture for Senate Democrats, suggesting that the president would have to get his approval above 50 percent by Election Day before they would be favored to hold the chamber. This is also consistent with what we’ve seen in polling, which shows the seven “red state” Democrats in truly severe states of distress, while Democrats in Iowa, Michigan, New Hampshire and Colorado are exhibiting surprising weakness. If these 11 seats are showing similar signs of weakness in November, Democrats will have an extremely difficult time holding the chamber. At Obama’s current 44 percent approval rating, we’d expect Democrats to lose somewhere between nine and 13 seats.
But let’s take it one step further. We’re probably right to be skeptical that Obama’s job approval will be, say, 55 percent on Election Day, just as it’s not likely to be 38 percent. Instead, let’s run simulations for his job approval. It has averaged 48.3 percent over his presidency, with a standard deviation of 4.35 percent. If we run our simulations around these values, we get the following overall distribution of outcomes:
Notably, there are situations where Democrats end up gaining seats. There are also, however, situations where the election turns into an absolute debacle for Democrats.
The most common outcome, however, is Democratic losses of between seven to nine seats. In about a third of the simulations there are more losses, and in about a third of the simulations, there are fewer.
Now, again, one might decide that, based on candidate quality and other issues, Democrats are poised to systematically end up on the high side of the probability calculus. I actually think this is probably correct. My general view is that this approach gets the odds right in the most commonly discussed races, especially since Republicans don’t seem poised to nominate weak candidates (for now). At the same time, though, weak Republican recruiting in places like Iowa and Minnesota, combined with unusually gifted Democratic incumbents in places like Virginia, probably means that the model overstates Democrats’ chances of losing more than eight seats.
One other possibility is that the relationship we’ve seen between job approval and Democratic outcomes won’t hold for this cycle. It’s been relatively strong over the past couple of elections, but that doesn’t mean it will continue. In fact, models that go back further in time give Democrats a much stronger chance of holding the Senate. My own sense is that, due to polarization, it now takes extremely unusual circumstances for a Democrat to win a state like Arkansas under a Democratic president (just as Lincoln Chafee couldn’t hold on in Rhode Island under a Republican president, despite being a very liberal Republican). But this might not hold true this year.
With all of that said, this is a very, very challenging map for Democrats. As things presently stand, the map probably makes them underdogs to hold the Senate. Barring some sort of change in the national environment or meltdown in the Republican nominations process — neither of which is impossible — Democrats are likely in for a very long night on Nov. 4.