Wave elections are remembered for the sheer number of seats flipped and of course the upsets, but the volume of close contests in them can be useful when looking ahead to the next cycle.
Forty-five House seats were decided by margins of five or less, almost all of them held by Republicans. Republicans held onto twenty-four of them and lost twenty and control of the House with them (North Carolina’s 9th District race remains up in the air and a new election is likely). Here’s their margins in 2016, 2018, and how President Trump performed in each three years ago:
| Congressional District | Current Representative | Trump Margin 2016 | 2016 R margin | 2018 R margin | Did incumbent run in 2018? |
| TX-22 | Pete Olson | 7.9% | 19.0% | 4.9% | YES |
| MT-AL | Greg Gianforte | 20.6% | 15.6% | 4.6% | YES |
| MI-06 | Fred Upton | 8.4% | 22.1% | 4.6% | YES |
| OH-01 | Steve Chabot | 6.6% | 18.4% | 4.4% | YES |
| PA-16 | Mike Kelly | 20.0% | n/a | 4.3% | YES |
| TX-10 | Michael McCaul | 9.1% | 18.8% | 4.3% | YES |
| OH-12 | Troy Balderson | 11.3% | 36.8% | 4.2% | NO |
| NY-01 | Lee Zeldin | 12.3% | 16.4% | 4.1% | YES |
| MO-02 | Ann Wagner | 10.3% | 20.8% | 4.0% | YES |
| CA-50 | Duncan Hunter | 15.0% | 27.0% | 3.4% | YES |
| IA-04 | Steve King | 27.4% | 22.6% | 3.3% | YES |
| KY-06 | Andy Barr | 15.3% | won uncontested | 3.2% | YES |
| TX-24 | Kenny Marchant | 6.2% | 16.9% | 3.1% | YES |
| TX-31 | John Carter | 12.7% | 21.8% | 2.9% | YES |
| PA-10 | Scott Perry | 8.9% | n/a | 2.6% | YES |
| TX-21 | Chip Roy | 10.0% | 20.5% | 2.6% | NO |
| PA-01 | Brian Fitzpatrick | -2.0% | n/a | 2.5% | YES |
| NE-02 | Don Bacon | 2.2% | 1.2% | 2.0% | YES |
| KS-02 | Steve Watkins | 18.4% | 28.3% | 0.9% | NO |
| IL-13 | Rodney Davis | 5.5% | 19.4% | 0.8% | YES |
| MN-01 | Jim Hagedorn | 21.3% | -0.7% | 0.5% | NO |
| TX-23 | Will Hurd | -3.4% | 1.3% | 0.4% | YES |
| NY-27 | Chris Collins | 24.5% | 34.4% | 0.4% | YES |
| NC-09 | NOT CERTIFIED | 11.6% | 16.4% | 0.3% | NO |
| GA-07 | Rob Woodall | 6.3% | 20.8% | 0.2% | YES |
| UT-04 | Ben McAdams | 6.7% | 12.5% | -0.3% | YES |
| CA-21 | T.J. Cox | -15.5% | 13.4% | -0.8% | YES |
| GA-06 | Lucy McBath | 1.5% | 23.4% | -1.0% | INC ELECTED IN 2017 |
| ME-02 | Jared Golden | 10.3% | 9.6% | -1.3% | YES |
| NJ-03 | Andy Kim | 6.2% | 20.4% | -1.3% | NO |
| SC-01 | Joe Cunningham | 13.1% | 21.8% | -1.4% | NO |
| OK-05 | Kendra Horn | 13.4% | 20.3% | -1.4% | YES |
| FL-26 | Debbie Mucarsel-Powell | -16.3% | 11.7% | -1.8% | YES |
| NY-22 | Anthony Brindisi | 15.5% | 5.4% | -1.8% | YES |
| NM-02 | Xochitl Torres Small | 10.2% | 25.4% | -1.9% | NO |
| VA-07 | Abigail Spanberger | 6.5% | 15.3% | -1.9% | YES |
| IA-03 | Cindy Axne | 3.5% | 13.7% | -2.2% | YES |
| VA-02 | Elaine Luria | 3.4% | 22.8% | -2.2% | YES |
| CA-39 | Gil Cisneros | -8.6% | 15.2% | -3.1% | NO |
| MI-08 | Elissa Slotkin | 6.7% | 16.8% | -3.8% | YES |
| CA-45 | Katie Porter | -5.4% | 17.2% | -4.1% | YES |
| MN-07 | Collin Peterson | 30.8% | -5.1% | -4.3% | YES |
| CA-10 | Josh Harder | -3.0% | 3.4% | -4.5% | YES |
| WA-08 | Kim Schrier | -3.0% | 20.4% | -4.8% | NO |
| IL-14 | Lauren Underwood | 3.9% | 18.6% | -5.0% | YES |
Data: DDHQ Elections, DailyKosElections (for President by CD)
Incumbency saved Republicans from a dozen additional losses but it wasn’t strong enough to hold things together and didn’t leave red reps immune: of the 20 closest Democratic House victories, only 7 were open contests.
If President Trump wins re-election, it’s reasonable to assume a few of the seats in the negative flip back to the GOP. It’s also safe to assume if he loses, many of those Republicans who endured last year’s wave won’t be lucky again. President Trump outran only a handful of Republican Representatives in 2016, and with the political sorting we saw then and since, his performance and that of his Congressional counterparts, I suspect, won’t deviate as widely.
Keep an eye on a number of these seats going into 2020. They are likely at the tops of each Party’s list for targeting/defending.