This year we are off to a late start; More balls in the air, especially gerrymandering games, and a busy terminology.
The House and Senate calculations are running for 2018, even though we’re still polishing the screen. Calculations are designed to pick up motion quickly. Here’s what’s worth noting: as of Labor Day, both indices have shown a diverging movement, about 2 percentage points, towards Republicans.
Now a word about Senate’s snapshot calculations and previews.
The House chart shows the moving average of the general congressional ballot: three or two weeks of probing in advance, whichever is greater and the 90% confidence threshold. It is a snapshot of current conditions as measured by the opinion polls. It records real changes in D-so-R’s opinion, as well as temporary changes in voter enthusiasm.
Compare this movement curve with my estimate of where the National House of Representatives vote needs to be controlled to flip, D + 6%. Finally, the chart shows an extrapolation based on special elections, which previously predicted the November result.
For most of the summer, the Democrats were supported to retake the House of Representatives, though not overwhelming. The threshold is high due to a combination of demographic patterns and partisan opposition. Currently, Democrats need 23 seats to gain control of the lower house. Without gerrymandering, they only need to get about 11 seats.
Since the beginning of September, the Internal Estimator has changed significantly and now shows control as a perfect change. Considering the special election results, the conditions may return to Democrats.
Is this movement a random movement? Probably not, since an independent calculation gives the same result: a snapshot of the Senate.
This is the average graph of the Senate’s overall distribution of results, from the 10 main races (AZ / FL / IN / MO / MT / MD / NJ / NV / TN / TX). The data comes from RealClearPolitics and electoral-vote.com. Because this calculation uses only polls, it yields the highest time resolution we can get. Again, notice the sudden change for Republicans starting in early September.
The movement of the Senate and the House of Representatives can be directly compared by calculating the meta margin of the Senate. Recall that meta-margin was defined as the number of polls that would have to change across the board to make controlling D-so-R a perfect kick. Currently, the meta margin is R + 2.8%. On Labor Day, it is R + 1.4%. That 1.4 point change is comparable to a two point change in the House calculation.
So far this year, the rule of thumb for 2018 is that the 1.7-point overall shift in Senate polls resulted in a 1-seat shift in the number of likely seats. With Senate control in the balance, small changes are more likely to happen.
However, one really important note: midterm voting errors can be huge. In 2014, the overall error was close to 5 points. So while Republicans are in favor of holding the Senate, the risk to their control is very real, maybe even 30% based on today’s snapshot.
What’s behind the September change? One obvious possibility is the nomination of the Kavanaugh Supreme Court, which has attracted the national attention. Trump’s approval rating continues to be surprisingly stable and low, and it’s no surprise that Republican intensity has faded. But with such a clear Supreme Court war, many voters may be reminded of why they supported the Republican Party in the first place. That will tend to fuel GOP voter enthusiasm.