Check out our maps and analysis comparing 2016's presidential and congressional results by district

by Stephen Wolf for Daily Kos Elections

Daily Kos Staff Emeritus

Tuesday, Jan. 31, 2017 Tuesday, Jan. 31, 2017 at 12:31:36pm PST

Map of the 2016 elections by winning presidential and congressional party

Daily Kos Elections recently published the last remaining state in our project to calculate the 2016 presidential election result for all 435 congressional districts. As the map above shows (see here for a larger version), of the 241 Republicans elected to the House, 23 represent seats that Hillary Clinton won, while 12 of the 194 House Democrats hold constituencies that back Donald Trump. This means that if Democrats want to retake the House next year, they’ll need to win most (if not all) the Clinton-GOP seats, hold onto their Trump-Democratic districts, and pick up a few Trump-Republican seats.

In this post, we’ll compare the presidential race with the congressional contest in each district to get a better idea of which House members outperformed their party’s presidential nominee, and which lagged behind—and could therefore struggle in 2018. As you follow along, you’ll also want to check out our comprehensive guide to the 115th Congress, which has presidential and congressional results for every district and state, along with member details and district demographics. (We’ve also separately mapped, graphed, and analyzed the presidential results by district, too.)

Regular geographic maps like the one seen at the top of this story tend to unfairly obscure cities with high population density and overemphasize sparsely populated rural areas. To account for that, we’ve also created cartogram versions of every map (like the one seen below) that display every district equally sized to give you a much better sense of proportions.

This map makes it far easier to see that there were almost twice as many Clinton-Republican districts than Trump-Democratic ones. Most of the Trump-Democratic districts are located in the Northeast and Midwest, where Trump did much better than other recent Republican nominees, while most of the Clinton-Republican seats are situated in the Sun Belt, where she improved upon Obama’s performance. Overall, just 35 districts split their tickets, a mere 8 percent of the total chamber.

Located along the state’s western border, Minnesota’s 7th District was Trump’s best district that voted for a Democrat. Thirteen-term Rep. Collin Peterson eked out a 52.5 percent to 47.4 percent win over an unheralded opponent as Trump carried his seat by 61.8 percent to 31 percent, a margin of 30.8 points. Peterson previously had the distinction of holding Mitt Romney’s best district of any House Democrat following the 2014 elections, but Romney “only” carried the seat by a 54-44 margin.

Florida’s Miami-based 27th District, which has a large Cuban-American population, was Clinton’s best district that nonetheless supported a Republican. Rep. Ileana Ros-Lehtinen prevailed by 54.9 percent to 45.1 percent against a flawed challenger even as Clinton romped to victory here by 58.6 percent to 38.9 percent, a 19.7 percent margin. Ros-Lehtinen and Peterson could find themselves high atop the other party’s target list in 2018.

Let’s next take a look at the full House results themselves.

The above map shows the congressional election margin in every district. Republicans won an overall 241-to-194 majority, six fewer seats than in 2014. A sizable 64 of 435 districts, or 15 percent, did not even feature both parties on the ballot, which as you will see below can sometimes confound analyses that compare the presidential and congressional results.

The histogram below, courtesy of Daily Kos Elections’ Daniel Donner, graphs every congressional district from the most Democratic to least Democratic—or in other words, from the biggest Democratic margin to the biggest Republican one.

Republicans won the seat in the middle (known as the “median district”) by a 12.8 percent margin, meaning that they won exactly half the seats by that margin of victory or greater. (That seat, Michigan’s 11th District in suburban Detroit, is unsurprisingly held by a Republican, Rep. Dave Trott.)

Although Democrats were briefly hopeful that Trump’s Access Hollywood tape scandal might put the House in play, Republicans easily maintained their majority. Gerrymandering and incumbency played a large role in preserving that majority, as you can see from the histogram. It has two distinct “modes,” or clusters, with results tending to show either a decisive Republican win or a decisive Democratic win. Only 32 districts had a margin within single digits—those short, light-colored bars in the very middle, between the taller but narrower red peak and the flatter but wider blue plateau.

The map below compares the congressional election margin with the presidential result in every district that had both major parties on the ballot. The 129 districts in blue saw the Democratic candidate exceed Clinton’s margin, while those 242 seats in red had Republicans who overperformed Trump’s margin.

Not only do aforementioned Democratic Rep. Collin Peterson and Republican Rep. Ileana Ros-Lehtinen hold the districts that were most hostile to their party’s presidential candidate, but both members also outran their ticket more than any other candidate for their respective parties. Peterson exceeded Clinton’s margin by 35.8 percent, while Ros-Lehtinen outran Trump’s margin by 29.5 points.

Astonishingly, two incumbents faced no major-party challenger even though the other party’s presidential ticket won their district. Democratic Rep. Ron Kind in southwestern Wisconsin’s 3rd District skated by with no Republican opponent even as Trump carried his district 49.3 to 44.8. Meanwhile, Republican Rep. Pete Sessions faced no Democratic foe in Texas’s 32nd District, located in northern Dallas, even as Clinton edged out Trump by 48.5 points to 46.6 points. But from another vantage point, the lack of opponents is not entirely shocking, since both districts saw a very sharp swing toward the presidential candidate who won then compared to 2012. (That is to say, Obama won Kind’s district and Romney won Sessions’.)

The next graph presents the same information as the previous map in the form of a scatterplot. Both presidential and congressional results were extremely correlated with one another. (For statistics gurus, the R² value was 0.91, which roughly matches 2012, and both election years saw the strongest correlation between congressional and presidential performance in generations.)

You might notice that Democratic winners tended to outrun Clinton’s margin, while Republican winners often exceeded Trump’s performance. As we’ll demonstrate below, much of that is a consequence of the incumbency bonus.

Our next map displays how the 194 districts that sent a Democrat to the House compared with the presidential result. A total of 95 Democratic winners outran Clinton’s margin, while 64 of them trailed the presidential ticket (35 seats had no Republican on the general election ballot). Democrats most notably exceeded Clinton’s margin in the Midwest and Northeast, while they lagged behind it in much of California.

While Rep. Collin Peterson improved on Clinton’s performance more than any Democratic winner, Rep. Brad Schneider underperformed Clinton’s margin by a greater amount than any Democrat who nonetheless won. He only defeated Republican Rep. Bob Dold by 52.6 percent to 47.4 percent in a rematch of their 2014 bout, even though Clinton carried Illinois’ highly educated North Shore 10th District by 62 points to 32.6 points, a disparity of 24.2 percent between their two margins.

As for the GOP, far more Republican winners outperformed their presidential ticket than Democrats did. Overall, 178 Republicans exceeded Trump’s performance, while just 34 trailed his margin (29 districts had no Democratic candidate).

While the aforementioned mentioned Ros-Lehtinen outpaced Trump’s margin more than any other Republican, Rep. Martha Roby underperformed his result more than any Republican who still won. Roby only prevailed by just 48.8 percent to 40.5 percent thanks in part to a conservative write-in challenger who soaked up 9 percent of the vote, while Trump carried her southeastern Alabama 2nd District by a 64.9 percent to 33 percent landslide. Roby’s 23.7-point underperformance of Trump’s margin is still pretty amazing, though, since it came against a completely unheralded Democratic opponent.

Of course, as we alluded to above, incumbency plays a large role in why congressional candidates often win more votes than their presidential ticket, so below we mapped out just the incumbent Congress members who were on the ballot for each party.

As seen in the above map, 85 Democratic incumbents outran Clinton’s margin, while 52 performed worse than she did, and 32 faced no Republican challenger.

Once again, Peterson topped Clinton’s margin more than any Democratic incumbent, while Rep. Jan Schakowsky lagged the presidential ticket more than any Democratic House member. Schakowsky won Illinois’ 9th District, located in Chicago and its northern suburbs, by 66.5 percent to 33.5 points, while Clinton carried the highly educated district by 70.1 percent to 24.9 percent for an overall disparity of 12.3 percent between the two Democrats’ margins.

The next scatterplot presents this same information graphically, making it much easier to see how closely related Democratic incumbents’ margins were to Clinton’s. Incumbency almost certainly played a decisive role in helping Democrats turn back Republican challengers in the seven Trump districts that they held onto.

Rep. Brad Ashford—the lone red dot above, tucked in right at the origin—was the only Democratic incumbent to suffer a general election loss against a Republican, doing so by just a 48.9 percent to 47.7 percent margin to now-Rep. Don Bacon, while Trump carried Nebraska’s 2nd District in Omaha by a 48.2 percent to 46 percent spread.

Mapping out the results for Team Red’s incumbents, the vast majority beat Trump’s margin, with 163 doing so, while only 29 members underperformed their presidential ticket (27 faced no Democratic challenger). As noted above, Ros-Lehtinen topped Trump’s margin more than any other incumbent from her party, while Roby lagged behind it more than any other Republican.

And once again, graphing the same information as contained in the previous map illustrates just how strongly Republican incumbents ran ahead of Trump’s margin, with only a handful underperforming him by any substantial amount.

Nonetheless, Democrats defeated six incumbents: John Mica in Florida’s 7th District, David Jolly in Florida’s 13th District, Bob Dold in Illinois’ 10th District, Cresent Hardy in Nevada’s 4th District, Frank Guinta in New Hampshire’s 1st District, and Scott Garrett in New Jersey’s 5th District. (These are the blue dots just above the X axis.)

Two of those incumbents, Mica and Jolly, saw their districts move several points to the left after a court ordered Florida to redraw its congressional map ahead of the 2016 elections, while Dold, as noted above, lost in a rematch to the man he ousted from office in 2014 even though he outran Trump’s margin by a giant 24.2 points last year. It just wasn’t enough.

Most impressively, Democrats managed to defeat two incumbents even though Trump won their districts. Garrett’s northern New Jersey 5th District supported Trump by 48.8 percent to 47.7 percent, but he lost to Democrat Josh Gottheimer by 51.1 percent to 46.7 percent. However, the GOP establishment was reluctant to spend money on Garrett, a very difficult member who notoriously announced the he wouldn’t aid the party’s House campaign arm over their support for openly gay GOP candidates. Guinta’s eastern New Hampshire 1st District, meanwhile, voted for Trump by 48.2 percent to 46.6 points, yet he lost to Democratic Rep. Carol Shea-Porter by 45.8 points to 44.4 points following a campaign finance scandal.

Finally, this last map displays only the districts that had no incumbent running in November. Democratic candidates topped Clinton’s margin in 15 seats, Republicans outran Trump’s performance in 27 districts, and five seats only had one of the two major parties on the ballot.

Virginia’s Scott Taylor outran Trump’s margin more than any other Republican, winning by 61.3 percent to 38.5 percent even as Trump only carried the Virginia Beach-based 2nd District by 48.8 percent to 45.4 percent, a 19.5-point disparity. (Democrats shamefully all but forfeited the seat, nominating a perennial candidate.) Meanwhile, Colleen Hanabusa edged out Clinton’s margin by more than any other Democrat, securing victory in the Hawaii’s Honolulu-based 1st District by 71.9 percent to 22.7 percent while Clinton won by just 63.1 points to 30.5 points for a 16.6 percent difference between the two margins.

On the flipside, Wyoming’s Liz Cheney lagged Trump’s margin more than any Republican in an open seat. She won the state’s only congressional district by a 62-30 margin even though it was Trump’s best state, giving him a 68.2 percent to 21.9 percent victory, for an overall gap of 14.2 percent between their margins. And for Democrats, Salud Carbajal trailed Clinton’s margin more than any other open-seat Democrat, winning California’s Santa Barbara-based 24th District by just 53.4 percent to 46.6 percent even as Clinton carried the district by 56.7 points to 36.5 points, for an overall disparity of 13.4 points between their margins. Carbajal, however, was the only one of these four candidates who actually faced a seriously contested race.

And as this last scatter plot of the previous map’s data demonstrates, open seat results were very strongly tied to the presidential result. Indeed, only two of those 47 districts split their tickets. Trump won northern Arizona’s 1st District by 47.7 percent to 46.6 percent, but Democratic Rep. Tom O’Halleran prevailed by 50.7 points to 43.4 percent against scandal-plagued Republican Paul Babeu. Nevada’s 3rd District, located in the suburbs south of Las Vegas, also backed Trump by 47.5 points to 46.5 points, yet elected Democratic Rep. Jacky Rosen by a 47.2 percent to 46 percent spread over flawed Republican nominee Danny Tarkanian.

Given how the country’s congressional districts exhibit a strong underlying bias against Democrats, Republicans maintain a large advantage in the number of incumbents, and the extremely strong correlation between presidential and congressional results in the last three elections, Democrats certainly face a very uphill battle to regain the House in 2018. Even if they were to hold the 194 seats they currently hold and flip all 23 Republican districts that supported Clinton, they would still fall one seat shy of a majority.

However, if Donald Trump’s deep unpopularity persists, it’s entirely possible that the upcoming midterm will become a backlash against the president’s party much like the last three midterms. This far out from the election, it’s simply too soon to rule out the possibility of major Democratic gains in 2018 despite Republicans’ systematic advantages.