This is Part 1 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.
As we get closer to election day, presidential polling will begin to expose the national political environment and how the country feels about the two parties. But because the presidential election is so far away and the Democratic primary is up in the air, the House generic ballot — which asks poll respondents to choose between a generic Republican and generic Democrat for the House — is a better measure of the nation’s feelings on the two parties than presidential polls.
Eventually, taking both of these indicators into account will give the best picture of where House Republicans and Democrats stand. As election day gets closer, I will start relying more heavily on presidential polls and start using the House generic ballot less to measure the national environment and more to understand if voters plan to distinguish between their presidential and congressional votes.
Specifically, the goal of this series is to determine what the presidential popular vote will need to be for:
- Republicans to be guaranteed to re-take the House
- Democrats to be guaranteed to hold the House
- Republicans to be likely (but not guaranteed) to re-take the House
- Democrats to be likely (but not guaranteed) to re-take the House
- Democrats and Republicans to be about equally as likely to control the House.
By the end of this series, the chart below will be filled. Today, though, the task is to fill in only the bottom-left portion of the graph — the presidential popular vote margin that Republicans will need to safely win control of the House. The percentages around the semi-circle represent margins over the opposing party in the presidential popular vote.
So, what margin do Republicans need in the presidential popular vote to safely win control of the House? Heading into the 2020 elections, Republicans will need to net at least 19 seats to win back the House. The current makeup of the House is 235 Democrats, 197 Republicans, one independent and two vacancies. One of these vacancies, NC-03, is a safe Republican seat, meaning Republicans effectively have 198 seats. The other vacancy, is NC-09, will have a special election next week due to election fraud tainting the 2018 election. Lastly, the independent is Justin Amash in MI-03, who renounced his Republican identity after clashing with Trump and the party after calling for impeachment.
I am going to be extremely conservative in this calculation, because I want a number that will ensure Republicans control of the House barring wild circumstances.
As I’m being very conservative, I’m going to build in a lot of room for error on the Republican side. The safeguards are:
- A 10-seat cushion. Meaning I am estimating what Republicans need to win 228 seats, not the bare-majority 218.
- Assuming that Republicans lose the four seats with candidates embroiled in scandal: Steve King (IA-04), Duncan Hunter (CA-50), Chris Collins (NY-27), Ross Spano (FL-15)
- Assuming that Democrats win every seat where Hillary Clinton won >50% of the vote in 2016.
Totaling these, in order to reach the “safe” zone, Republicans need to win 33 additional seats: 19 to take the majority + 10 seat cushion + 4 to make up for seats lost due to scandal.
To find out which 33 seats will be easiest for Republicans to flip, we will take several things into consideration. The presidential popular vote that Republicans will need to take that 33rd seat will be our margin for them to “safely” take the House.
Here are the variables we will take into account:
- 2018 margin. This will be the baseline for the 2020 results.
- Incumbency advantage. FiveThirtyEight estimates that incumbents have a 2.7% incumbency advantage. So, for candidates who were incumbents before 2018, they will get no additional boost. Candidates who won an open seat, will get this 2.7% boost. Candidates who beat an incumbent in 2018 will get double the 2.7% (5.4%), to account for the incumbency advantage of their opponent that they overcame in that election.
- 2016 Presidential Vote: Again, we will assume that the Republican loses in any seat in which Clinton won > 50%. These are highlighted in blue.
- The 2018 midterm’s national environment. Because the environment leaned 7.3% in Democrats’ favor, this will be subtracted from the Democratic candidate’s margin.
The chart below shows, in order, which Democratic seats Republicans are most likely to win, given our conditions and assumptions. The districts highlighted in blue are ones in which Hillary Clinton won >50%, which this overly-cautious projection model assumes that Democrats will win.
The 33rd seat that Democrats would flip is TX-32 in northeastern Dallas County. This seat is currently held by Collin Allred, who beat an incumbent by 6.5%. If we adjust for incumbency (+5.4%) and the Democratic environment of 2018 (-7.3%), we find that, in a neutral environment, Allred could expect to win his district by 4.6%. Therefore, Republican will need a 4.7% lead in the national environment, measured by the presidential popular vote, to safely win the House.
Keep in mind how many safeguards were build into this: a 10 seat margin, assuming Republicans lose four incumbent-held seats due to scandal and giving Democrats every district where Clinton won >50%. Therefore, if Republicans clear the 4.7% hurdle, they have the House all but guaranteed in the bag.
So, now we can fill in the first part of our chart! The arrow points to the newly filled in projection. We know that Republican’s will take the House (barring something crazy) if they win the presidential popular vote with anywhere between a 100% margin and a 4.7% margin.
The next few weeks will be dedicated to filling in data for the rest of the chart, which will become more useful as the presidential election nears and the national environment starts to become clear.