11 days ago, JMC assessed the partisan climate of 435 US House races using a combination of election and polling data. In making these assessments, JMC considered the electoral reality that the “split ticket” voter (i.e, a voter who supports candidates from different parties for Presidential and “downballot” races such as Congressional races) has been in decline ever since the early 1990s, and with voters’ being increasingly likely to vote the same way (i.e., a “straight ticket” voter) both in Presidential and Congressional races, the 2016 Presidential vote for all 435 U.S. House districts is a good place to start for (theoretically) assessing how “solid” a House district is for either party. The following criteria are used:

Part One: Defining JMC’s “watch list”:

Most vulnerable: a House Republican represents a district that gave President Trump less than 50% of the vote in 2016 (or a Democrat representing a district President Trump carried with an absolute majority). 41 districts meet this criteria (37 represented by Republicans, 4 by Democrats). These districts narrowly supported Hillary Clinton 47-46% (about the national popular vote), and in a partisan wave, these districts are likely the first ones to flip;

Moderately vulnerable: a House Republican represents a district that voted between 50-55% for President Trump in 2016 (or a Democrat representing a district President Trump carried with a plurality of the vote). An additional 60 districts meet this criteria (52 represented by Republicans, 8 by Democrats). These districts overall supported Trump 52-43% over Hillary Clinton, so these districts hypothetically (without taking into consideration candidate strengths/weaknesses) have “Republican votes to spare”, and would therefore be less likely to flip in the “straight ticket” environment of today, unless the partisan wave were substantial;

Minimally vulnerable: a House Republican represents a district that voted between 55-60% for President Trump in 2016 – except under extraordinary circumstances, the assumption here is that even if the Republican candidate is weak, there are more than enough “Republicans to spare.” 52 districts (all Republican held) meet this criteria, and these districts supported Trump 57-38% over Hillary Clinton;

Given the detailed criteria above, JMC is watching 153 House districts (141 held by Republicans, 12 by Democrats) – the assumption for the remaining 282 House districts is that the Trump (or Clinton) percentage is high enough for it to be extremely unlikely for any of these seats to flip.

Part Two: Applying JMC’s “watch list” to actual (election and polling) data:

Given that the Presidential percentage is more theoretical in nature, what does actual polling data (or in the case of nonpartisan primaries in California and Washington State, primary election data) say? (Caveat: polling/election data is only available for 57 of the 153 House seats placed on the “watch list”)

Most vulnerable seats (29 have poll and/or primary election data)

• 4 safe Republican seats (was 5 last week);
• 12 Republicans and one Democratic seat are too close to call  – “too close to call” meaning the leading candidate is ahead by less than 5 points (was 10 Republican and 1 Democrat last week);
• 12 Republicans are trailing by 5 or more points, and therefore, these seats are likely to “flip” (was 5 Republicans last week);

Moderately vulnerable seats (19 have poll and/or primary election data)

• 9 seats are safe Republican (was 6 last week);
• 1 seat is safe Democratic (no change);
• 7 Republican seats are too close to call (was 5 last week);
• 2 Republicans are trailing by 5 or more points (was 1 last week);

Minimally vulnerable seats (9 have poll and/or primary election data):

• 5 are safe Republican (no change);
• 4 Republican seats are too close to call (was 3 last week). 

To summarize, this sample of 57 House races (out of a population of 153 House districts) where polling and/or election data is available shows the following:

• 18 safe Republican and 1 safe Democratic seats (was 16 Rep, 1 Dem last week);
• 23 Republican and 1 Democratic held seats are “too close to call” (was 18 Rep, 1 Dem last week);
• 14 Republicans trail by 5 or more points.

October 4 House Scorecard

If this sample of 57 were extrapolated to the entire population of 153 seats on JMC’s “watch list”, that would suggest a Republican loss of 21 seats, with 60 Republican (and 4 Democratic) seats that are too close to call.

What is the political complexion of those 24 seats that are “too close to call” ? These seats on average voted 49-45% for President Trump (while supporting the Republican incumbent in 2016 with an average of 57% – those Congressional Republicans ran 8 points ahead of Donald Trump in 2016), so these “tossup seats” are slightly more Republican friendly than the nation as a whole (the 2016 national popular vote was 48-46% for Clinton).

For the 14 seats where Republicans are trailing, Clinton carried these districts 48-46% (exactly what she received in the national popular vote), while GOP incumbents received on average 54% of the vote in their 2016 campaign – in other words, GOP incumbents ran on average 8 points ahead of President Trump, and whether they can do so this year will determine whether they can survive or be inundated by a partisan wave.

As additional House race polls are released, this analysis will be revisited; the point of this analysis was to show (using available Presidential, primary, and polling data) why Republicans face the very real possibility of losing their House majority for the first time since 2006.