How stable is GOP control of the US House of Representatives, now that midterm elections are six weeks away? To objectively answer this question, JMC has evaluated all House districts that are in (or can be put into) play by using a combination of election and polling data.

To put JMC’s analysis in proper context, 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 1992, and with voters’ being increasingly likely to vote the same way (i.e., a “straight ticket”) in Presidential and Congressional races, the 2016 Presidential vote for all 435 U.S. House districts is a good place to start for assessing how “solid” a House district is for either party. The following criteria are used for assessing each district:

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 what the national popular vote was), and in a partisan wave, these districts would likely be 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 some “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 mentioned above, JMC is watching 153 House districts (141 held by Republicans, 12 by Democrats) for the remainder of the election cycle. For the remaining 282 House districts, the Trump or Clinton percentage is high enough to where it’s extremely unlikely that that any of these seats would ever flip. This (House seats’ being “too Democratic/ Republican to flip”) was also the case in previous wave years.

The data above, however, is more theoretical in nature. What about actual polling data (or in the case of nonpartisan primaries in California and Washington State, actual primary election data)? (Caveat: polling/election data is only available for 42 of the 153 House seats placed on the “watch list”)

Most vulnerable seats (21 have poll and/or primary election data)

• 5 seats are safe Republican;
• Too close to call for 10 Republicans and one Democrat  – “too close to call” meaning the leading candidate is ahead by less than 5 points;
• 5 Republicans are trailing by 5 or more points, and therefore, these seats are likely to “flip.”

Moderately vulnerable seats (13 have poll and/or primary election data)

• 6 seats are safe Republican;
• 1 seat is safe Democratic;
• Too close to call for 5 Republicans;
• 1 Republican is trailing by 5 or more points;

Minimally vulnerable seats (8 have poll and/or primary election data):

• 5 are safe Republican;
• Too close to call for 3 Republicans.

To summarize, this sample of 42 House races (out of a population of 153 House districts) where polling and/or election data is available shows the following:

• 16 safe Republican and 1 safe Democratic seats,
• 18 Republican and 1 Democratic held seats are “too close to call”
• 6 Republicans trail by 5 or more points.

If this sample of 42 were extrapolated to the entire population of 153 seats on JMC’s “watch list”, that would suggest a Republican loss of 22 seats, with 66 Republican (and 4 Democratic) seats that are too close to call.

What is the political complexion of those 19 seats that are “too close to call” ? These seats on average voted 48-45% for President Trump (while supporting the Republican incumbent in 2016 with an average of 55%), 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 6 seats where Republicans are trailing, Clinton carried these districts 48-45% (almost exactly what she received nationally), while GOP incumbents received on average 53% of the vote in their 2016 campaign – in other words, they ran on average 8 points ahead of President Trump, but it’s questionable whether they can do so again this year.

This means that in an era of straight ticket voting, these “too close to call” seats will determine who controls the US House, and given their marginal nature politically, the 2016 Trump vote will not by itself keep these seats in the Republican column – some ticket splitting has to occur.

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.