FORECASTING THE HOUSE: PROJECTIONS BASED ON THE PRESIDENTIAL POPULAR VOTE

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This is Part 3 in a short series projecting which party will win the House in 2020 given different possible presidential outcomes. Because it is a presidential election year and given the intensity of partisanship and increasing number of straight-ticket voters, the presidential results will be the best measure of the national environment and the most important factor in the House elections. This series will explore what those presidential results will mean for the House and which party can expect to win a majority of seats based on the various possibilities. You can find Part 1 here and Part 2 here.

This post is going to complete the series forecasting who will control of the House in 2020 based on the national environment, which is best measured by the presidential popular vote. Democrats currently hold 235 seats, Republicans hold 199, and Justin Amash is the lonely independent in MI-03. This means that Democrats can afford to lose, at most, net 17 seats.  This graphic, from our previous post, shows where we left off and what we still need to finish. 

The next chart shows, according to our model, the order that Democratic held seats would flip to Republicans. The model’s calculation uses the 2018 midterm margin, the changes in incumbency status from 2018 to 2020, and an adjustment for the 7.3% Democratic environment of the 2018 midterms. The last column shows the projected margin for the district in a neutral national environment, with positive numbers indicating a Republican victor and negative numbers indicating a Democratic win. Finally, the districts highlighted in red are ones where Donald Trump won >51% of the vote, which will be important for our projections below.

Safely Democratic
Let’s start with what national environment Democrats need to “Safely” hold the house. As with “Safely Republican”, I am going to build in a lot of safeguards here, setting a high bar for the House to be considered safe. These include:

  • Building in a 10 seat Democratic cushion, meaning that, for this calculation, Democrats can only lose seven seats, putting the House at 228D to 206R.
  • Assuming that Democrats lose the eight districts that Trump won by >51%.1In the “Safely Republican” calculation we assumed that Republicans lost any seat that Clinton won by >50%, not >51% like we assume here. The bar is a bit higher here because 1) There are a lot more seats held by Democrats that Trump won and Democrats are very unlikely to lose all of them. 2) A lot of these seats are in suburban zones that are swinging heavily away from Republicans.

Taking these two precautions, we already have Democrats losing eight seats — one more than our Safe model will allow. This means that they will have to win back one seat. The presidential popular vote they need to be able to expect to win this seat will be the bar they need to clear to Safely control the House.

So which House seat currently occupied by Republicans will be easiest for Democrats to flip? According to our model, the easiest seat for Democrats to flip will be TX-23.

This seat spans a majority of Texas’s western border with Mexico and is 62% Hispanic, a key demographic for Democrats. The Republican incumbent, Will Hurd, has been a uniquely strong incumbent, but barely squeaked out a 0.4% win and is not running for reelection next year. According to our calculation2Start with Republicans’ 0.4% 2018 margin. Adjust in Republicans favor 7.3% for the Democratic leaning environment in the 2018 midterms. Give Democrats a 2.7% boost due to the Republicans losing their incumbency advantage., Republicans could expect to win this seat by 5% in a neutral environment, meaning that Democrats need a 5.1% favorable environment to win this seat and be considered “Safe” to keep control of the House.

Likely Democratic
Moving to the “Likely Democratic” category, we are going to ease up on the safeguards a bit. The precautions now include:

  • Building in a 5 seat Democratic cushion, meaning that, for this calculation, Democrats can only lose 12 seats, putting the House at 223D to 211R.
  • Assume Democrats lose the eight districts where Trump won > 51%.

With these guardrails in place, Democrats can still afford to lose four more seats. The easiest of which (according to our model) would be NM-02, UT-04, CA-39, CA-21. The next seat in line, GA-06, is the one Democrats would need to hold onto. It would be 0.9% R in a neutral environment, meaning Democrats need to have a 1% advantage to make control of the House “Likely Democratic”

Toss Up
For our “Toss-Up” category we are going to find the tipping point seat — the one that would tip control of the House away from Democrats. Given the current breakdown of the House with one independent, there are actually two tipping point seats — one that would tip the House to a 217 – 217 tie and one that would tip it to a 218 – 216 Republican majority. The 18th and 19th seats that Republicans flip are these two “tipping point” seats. The 18th most likely seat to flip is Florida 27th and the 19th most likely is MI-08. These two districts would lean 1.9% and 1.4% Democratic in a neutral national environment, making these the boundaries for the toss up category.

Wrapping Up
Now that we have all the data, we can fill in the rest of our chart.  

A neutral environment, meaning the presidential popular vote is 50/50, falls into the “Lean Democrat” category. This is mostly due to their incumbency advantage in many of the most competitive districts that could determine control of the House. Democrats also have an advantage in the 1-3% margin range. If the national environment is 1%-3.3% in Democrats favor, they are “Likely” to win the House, but if it is a similar Republican leaning environment, the House a Toss Up, Lean Republican and even Lean Democrat. If either party wins by around 5% or more, though, it looks like the House is theirs.

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