Date District Dem Running Held By Prior Margin Clinton Margin Obama Margin Dem Win Prob 2/20 KY

HD-49 Linda Belcher R -1% -49% -33% 7% 2/27 CT

HD-12 Philip Young R -25% 2% 6% 68% 2/27 NH

HD-

Belknap 3 Philip Spagnuolo R -8% -12% 1% 64% 2/27 KY

HD-89 Kelly Smith R U -62% -56% 0% 3/6 OK

HD-51 Charles Murdock R -56% -65% -57% 0% 3/13 TN

SD-14 Gayle Jordan R -49% -44% -35% 0% 3/27 AL

HD-21 C. Terry Jones R -35% ? ? ? 4/3 MA

HD-2 TBD D U 9% 11% 97% 4/10 FL SD-31 Lori Berman D U 25% ? ? 5/1 FL

HD-39 Ricky Shirah R -24% -19% -12% 24% 5/1 FL

HD-11 Javier Fernandez D 2% 14% 1% 95% 5/1 MA

SD-1 TBD D U 65% 62% 100% 5/15 AL

HD-4 Juanita Allen Healey R U ? ? ? 5/15 AL

SD-26 TBD D U ? ? ? 5/15 PA

HD-48 TBD D U -15% -8% 54% 5/15 PA

SD-17 TBD R -22% -3% -13% 47% 5/22 AR

SD-16 Teresa Gallegos R U ? -46% ? 5/22 AR

SD-29 Steven McNeely R U ? -57% ? 6/5 CA

HD-39 TBD D U 55% 50% 100% 6/5 CA

HD-45 TBD D -33% 40% 29% 98% 6/5 CA

HD-54 TBD D 63% 75% 70% 100%

Background

“They’re winning elections in places where they shouldn’t be,” former Trump campaign Corey Lewandowski said of Democrats at a recent campaign rally.

For once, Lewandowski is right.

He was campaigning for James Buchanan, a Republican running for a State Legislative seat in Florida that had voted for Trump in 2016 and Romney in 2012. But last week, the district elected a Democrat — Margaret Good — by a comfortable seven-point margin.

That marked the 36th state legislative seat flipped from the Republicans to the Democrats since Trump took office. In the same period, Republicans have flipped only four seats from Democrats. And about half of those Dem flips have resulted from special elections, of which there are at least 30 more to come this year.

Much has been written about whether these special election flips are necessarily predictive of a coming Democratic wave — a topic I’ll be sure to discuss later on. But for now, I want to address the most immediate question: where should Democrats target next?

To answer this question, I’ve assembled the table above of upcoming special elections and estimated Democratic win probabilities.

Training Data

I made use of data collected from 222 contested elections in the Trump era. These include:

83 special elections across 25 states. The vast majority (93%) were state legislative special elections, but I also included the six Congressional/Senate special elections of the Trump era.

63 races from the regularly scheduled elections in Virginia. Of these, 60 were contested House of Delegates races, and three were statewide races (Governor, Lieutenant Governor, Attorney General).

76 races from the regularly scheduled elections in November. Of these, 37 were State Assembly races and 38 were State Senate races. The governor’s race was also included. Because NJ elects two General Assembly representatives per district, the results were combined into a single Democrat vs. Republican vote share in each district, represented as a single race in the dataset.



The dataset can be found here. Much of the data was sourced from data provided by Ballotpedia, Wikipedia, Daily Kos, and Statistical Atlas. Please reach out if you find any errors!

Model

I built a simple linear regression model to predict Democratic margin in each of these 222 races, using a simple set of predictors:

This model achieves a very high R2 value and the associations point in the expected direction. A few notes:

The “Special” variable denotes whether it was a special election. As we expect, this is a significant positive predictor of Democratic margin. Specials typically have low turnout; as a result, the party out of power often over-performs because its voters are more motivated to come to the polls.

“directionalIncumbency” is a variable that takes on the value of +1 for Democrat incumbents, -1 for Republican incumbents, and 0 for races without an incumbent. The incumbency effect we see is small (about 3% of the vote), but statistically significant.

In 78 of the elections, the seat was uncontested the last time it was up; as a result, we have no prior margin. For these seats, we impute what the margin “would have been” using a model based on the holding party and Obama’s 2012 margin. One could fault this approach in noting that uncontested seats are fundamentally unlike contested seats (e.g. parties don’t contest seats in cases where they don’t think they have any shot of winning). Thus, our imputed values may underestimate the vote share of the party holding the seat, had it actually been contested. This is a valid criticism, but observe that the dominant reason for not contesting a seat is the existence of a strong incumbent. Since we seek to model special elections (where there is not an elected incumbent), the underestimation is likely less of a concern.



Prediction Methods

To estimate the Democratic win probability, we apply the model to upcoming special elections. We then generate prediction intervals via normal theory, and take the mass of the prediction interval above 0 as our estimate of the probability of a Democratic victory.

Prediction intervals are typically used for uncertainty quantification, and it’s fair to question whether they can rightly be interpreted as a probability in this manner. My assumption is that this method provides a reasonable proxy for the Democrat’s probability of victory, and does a better job capturing the threshold effect of elections than would a purely probabilistic prediction (e.g. from a logistic regression).

Results

Predictions are given above. As of right now, I’ve been unable to source some needed presidential results to make projections in Alabama, Arkansas, and Florida. I’ll be looking to get that data soon. Any prior Democratic margin denoted “U” means the seat was uncontested last time it was up.

The model gives Democrats a great chance of flips in two special elections in just eight days: Phillip Young in Connecticut House District 12 and Philip Spagnuolo in New Hampshire House District Belknap 3. Consider donating to these candidates!

A few other thoughts:

The model is probably underestimating Linda Belcher’s chances tomorrow. She held this seat as recently as 2016 even as it voted Republican at the top of the ticket. She is a strong candidate and may well pull off an upset.

While I’m bullish on Young, note that Democrats have been underperforming in Connecticut all year, likely due to the unpopularity of Democratic governor Dan Malloy. I’d say this race is much more of a tossup than the model might otherwise project.

Democrats have some great chance in Pennsylvania and Florida later this year. Consider donating to Ricky Shirah and keep an eye on the PA primaries!