We’ve spilled plenty of digital ink on where Democrats made gains in the House, so now we are going to look more closely at the 200 seats the Republicans won. And we’ll use how a district voted for President Trump in 2016 in addition to a district’s population density as a guide. Why?

Not every district that voted heavily for Trump in 2016 was off limits to Democrats in 2018. Although, there was a point of no return — Democrats didn’t pick up a single district where Trump won 55 percent of the vote or more. Conversely, where Trump won less than 45 percent of the vote in 2016, no GOP candidate won in 2018.

But districts in the middle, where Trump won between 45 and 55 percent of the vote in 2016, formed the battleground for 2018 House contests: Democrats won 43 seats in this group, flipping 27 of them; Republicans flipped only two, winning 56 such seats altogether.

But many of these races were close — in the 56 that the GOP won, 38 had a single-digit margin of victory. Knowing the makeup of these districts is helpful in understanding where the Democratic Party may or may not have a chance of winning in the future. We can use the U.S. Census Bureau’s regional definitions to place districts geographically and CityLab’s Congressional Density Index to categorize how urban or rural districts are.

One immediate observation is that this group of districts is largely suburban. And while suburban seats proved to be the Democrats’ most fruitful territory in 2018, the GOP still managed to hold on to 30 seats in suburban districts where Trump won 45 to 55 percent of the vote in 2016.

Purplish Republican districts are more suburban Districts where Republicans won in 2018 and where Trump received 45 to 55 percent of the vote in 2016, grouped by density type Number of districts Where Trump won 45 to 55 Pct Region Rural Suburban Urban South 8 12 1 West 9 6 0 Midwest 5 8 0 Northeast 3 4 0 Total 25 30 1 The three-category density definition is based on a simplification of CityLab’s six-category scale of district density. The two most rural categories (Pure Rural and Rural-Suburban Mix) are combined into “Rural,” the two most suburban categories (Sparse Suburban and Dense Suburban) are combined into “Suburban,” and the two most urban categories (Urban-Suburban Mix and Pure Urban) are combined into “Urban.” Sources: CITYLAB, DAILY KOS, DAVE WASSERMAN, U.S. CENSUS BUREAU

Roughly two-thirds of these suburban districts are in the South and West, two regions that cover parts of the Sun Belt, a region where many Democrats hope to make further inroads in the future. In the South and West, Democrats won just 7 predominantly suburban seats in districts where Trump got between 45 and 55 percent of the vote, compared to 18 such seats for the GOP. Still, the GOP won 56 total seats in districts where Trump got around half the vote, but because they won by only narrow margins in some places, including some suburban areas, these might be districts where Democrats will try to compete in the future.

If we define competitive districts as those where the winning candidate’s margin of victory was in the single digits, 38 of the 56 middle-ground districts that Republicans won were decided by competitive margins, which means that if circumstances had been different — for example, if an incumbent had retired or a stronger Democratic candidate had run — some of those races might have gone the other way. The other 18 districts were won by 10 or more points, however.

Narrow Republican victories The 38 districts where Republicans won by less than 10 points in 2018 and where Trump won 45 to 55 percent of the vote in 2016 2018 Winner District Density Trump share Inc. Party Name Inc.? Margin GA-7 Suburban 51.1% R Rob Woodall ✓ R+0.2 NC-9* Suburban 54.4 R Mark Harris R+0.3 TX-23 Rural 46.4 R Will Hurd ✓ R+0.4 MN-1 Rural 53.3 D Jim Hagedorn R+0.5 IL-13 Rural 49.7 R Rodney Davis ✓ R+1.2 NE-2 Suburban 48.2 R Don Bacon ✓ R+2.0 PA-1 Suburban 47.1 R Brian Fitzpatrick ✓ R+2.5 PA-10 Suburban 52.3 R Scott Perry ✓ R+2.7 TX-21 Suburban 52.5 R Chip Roy R+2.8 TX-31 Suburban 53.5 R John Carter ✓ R+3.0 TX-24 Suburban 50.7 R Kenny Marchant ✓ R+3.2 KY-6 Rural 54.7 R Andy Barr ✓ R+3.2 CA-50 Suburban 54.6 R Duncan Hunter ✓ R+3.6 MO-2 Suburban 52.6 R Ann Wagner ✓ R+4.0 TX-10 Rural 52.3 R Michael McCaul ✓ R+4.0 OH-12 Suburban 53.2 R Troy Balderson ✓ R+4.2 OH-1 Suburban 51.2 R Steve Chabot ✓ R+4.2 MI-6 Rural 51.3 R Fred Upton ✓ R+4.6 TX-22 Suburban 52.1 R Pete Olson ✓ R+5.0 WA-3 Rural 49.9 R Jaime Herrera Beutler ✓ R+5.3 NC-2 Rural 53.2 R George Holding ✓ R+5.5 MN-8 Rural 54.2 D Pete Stauber R+5.5 CA-22 Suburban 52.1 R Devin Nunes ✓ R+5.9 NC-13 Rural 53.4 R Ted Budd ✓ R+6.0 FL-15 Suburban 53.1 R Ross Spano R+6.0 NY-1 Suburban 54.5 R Lee Zeldin ✓ R+6.1 NY-24 Rural 45.3 R John Katko ✓ R+6.2 AR-2 Rural 52.4 R French Hill ✓ R+6.3 VA-5 Rural 53.4 R Denver Riggleman R+6.5 AK-1 Rural 52.8 R Don Young ✓ R+6.6 NY-2 Suburban 53.0 R Pete King ✓ R+6.6 TX-2 Suburban 52.4 R Dan Crenshaw R+7.3 TX-6 Suburban 54.2 R Ron Wright R+7.7 CO-3 Rural 52.0 R Scott Tipton ✓ R+7.9 FL-18 Suburban 53.3 R Brian Mast ✓ R+8.6 CA-4 Rural 54.0 R Tom McClintock ✓ R+8.6 FL-16 Suburban 53.7 R Vern Buchanan ✓ R+9.1 WA-5 Rural 52.2 R Cathy McMorris Rodgers ✓ R+9.5 * The results of this race have been called into question by allegations of fraud. Sources: CityLab, Daily Kos, Dave Wasserman

Of course, part of what we’re seeing could be because this midterm cycle was quite favorable for Democrats — the party won the national House popular vote by more than 8 points. Who knows what the national environment might look like in 2020 — if the pendulum swings back toward Republicans, the GOP may easily hold these seats next time around, but if the national environment continues to benefit Democrats, they might be able to win some of these districts, especially some of the 30 predominantly suburban ones. Many of the 25 rural districts might be harder to pick up, however.

If we look at the makeup of the 144 districts where Republicans won in 2018 and where Trump won 55 percent or more of the vote in 2016 — a group in which Democrats didn’t make a single gain in 2018 — you’ll note there aren’t many suburban districts. In fact, 124 (or 86 percent) are rural. This is the area where Democrats have struggled most to gain in recent years.

Trump’s base is largely rural Districts where Republicans won in 2018 and where Trump received 55 percent or more of the vote in 2016, grouped by density type Number of districts where Trump won 55 Pct or more Region Rural Suburban Urban South 71 11 0 Midwest 38 3 0 West 8 4 0 Northeast 7 2 0 Total 124 20 0 The three-category density definition is based on a simplification of CityLab’s six-category scale of district density. The two most rural categories (Pure Rural and Rural-Suburban Mix) are combined into “Rural,” the two most suburban categories (Sparse Suburban and Dense Suburban) are combined into “Suburban,” and the two most urban categories (Urban-Suburban Mix and Pure Urban) are combined into “Urban.” Sources: CITYLAB, DAILY KOS, DAVE WASSERMAN, U.S. CENSUS BUREAU

What’s more, 82 of these districts are located in the South, which remains the most Republican region in the country. This may seem at odds with the earlier comment about Democrats and their hopes for a breakthrough in the South and West in 2020, but a lot depends on just how rural these districts are.

As expected, Democrats weren’t as competitive in these more GOP-leaning districts. But what’s striking is just how few of these races were remotely close. Just 10 of the 144 Republican-won districts where Trump garnered 55 percent or more of the vote were won by a single-digit margin.

Very few strongly pro-Trump rural districts were competitive The 10 districts where Republicans won by less than 10 points in 2018 and where Trump won 55 percent or more of the vote in 2016 Winner District Density Trump share Inc. Party Name Inc.? Margin NY-27 Rural 59.7% R Chris Collins ✓ R+0.6 KS-2 Rural 55.8 R Steve Watkins R+0.7 IA-4 Rural 60.9 R Steve King ✓ R+3.3 PA-16 Rural 57.9 R Mike Kelly ✓ R+4.3 MT-1 Rural 56.5 R Greg Gianforte ✓ R+4.6 IL-12 Rural 55.0 R Mike Bost ✓ R+6.6 MI-7 Rural 55.7 R Tim Walberg ✓ R+7.6 TX-25 Rural 55.1 R Roger Williams ✓ R+8.9 IN-2 Rural 59.3 R Jackie Walorski ✓ R+9.7 CA-1 Rural 56.2 R Doug LaMalfa ✓ R+9.9 Sources: CityLab, Daily Kos, Dave Wasserman

And three of these races might not have been competitive if not for controversial GOP candidates. The narrowest Republican win was New York’s 27th, where indicted Rep. Chris Collins barely survived to win another term. Controversial Rep. Steve King also had a close call in Iowa’s 4th, defeating a well-funded opponent by just 3 points. But Republicans held on in these districts, even in an open-seat race in Kansas that was on the lower end of Trump support (56 percent in 2016) and featured a somewhat scandal-plagued Republican candidate. Democrats managed to keep one seat in a district that voted at least 55 percent for Trump, but it took 14-term Rep. Collin Peterson of the Minnesota 7th — one of the most moderate Democrats in the House — to do so, and he won by just 4 points.

The 2018 results suggest that Democrats can win, or at least be very competitive, in districts where Trump won 45 to 55 percent of the vote. But many of these districts are predominantly suburban. Outcomes in more rural districts where Trump won 55 percent or more of the vote suggest that it will take special circumstances — such as a scandal-ridden GOP incumbent or a longtime Democratic incumbent — to overcome the strong partisan forces boosting Republicans in those seats. While it’s not necessarily surprising, the fact that Democrats did not come close to winning most of these seats shows just how difficult conservative terrain has become for Democrats to navigate, even in the midst of a historic blue wave.