Just under a year before the 2018 midterm elections, Democratic prospects for gaining the 24 net seats they need to take control of the U.S. House of Representative are getting stronger. Aside from a number of long-in-advance indicators like presidential approval ratings and the congressional generic ballot, the 2017 election returns, capped by high-profile Democratic wins in Virginia and elsewhere on November 7, have provided objective evidence that Democrats are regularly exceeding expectations based on past performance (if not always meeting last-minute expectations of big wins). But you win elections in particular places and one at a time, and at the level of individual races, Republicans retain a lot of advantages that could keep them in control of the House even if they lose the national popular vote.
Republicans also have a lot of exposure, having made a net gain of 68 House seats in the last three elections. This can matter even more than presidential approval ratings: In 2010, Obama’s pre-midterm approval rating was 45 percent, but his party — engorged by big House performances in 2006 and 2008 — lost 63 seats. Four years later, Obama’s approval ratings were sharply lower, at 40 percent, but his party only lost 13 net House seats.
Related: Tracking the Most Competitive House Races in the 2018 Midterms
A dynamic, monthly breakdown of the most competitive districts
The big-picture factors favoring Democrats are clear. The party controlling the White House almost always loses House seats in midterms; the two exceptions in recorded history occurred in years in which the presidents in question were enjoying very high approval ratings (Clinton at 66 percent in 1998 and George W. Bush at 63 percent in 2002). Since 1946, the average midterm House losses for presidents with approval ratings under 50 percent has been 36 seats. President Trump’s approval ratings (using the RealClearPolitics polling averages as a benchmark) have never topped 50 percent, and have mostly bounced around the low side of 40 percent since the spring.
The other big indicator for House races is the generic congressional ballot: a polling question that simply measures partisan voting intentions for upcoming congressional elections. According to FiveThirtyEight’s Harry Enten, the final generic ballot before midterm elections is on average as accurate as final presidential polls, hitting within 2 percent of the actual national House popular vote. The generic ballot can, of course, change significantly during the final year of a midterm cycle; at this point in 2009, for example, a CNN survey gave Democrats a six-point advantage in the generic ballot; the final RealClearPolitics average just before the 2010 midterms favored Republicans by 9.4 percent. But such big movements tend to occur in synch with presidential approval ratings, and beyond that, the usual trend is away from the president’s party, as in 2010.
The current RealClearPolitics generic ballot average gives Democrats a 10.2 percent advantage. The gap has been slowly increasing throughout 2017; six months ago it was at 5.8 percent.
Special (and regular off-year) elections in 2017 have shown a similar Democratic advantage. In an analysis of 38 such contests (mostly for state legislative seats), Daniel Donner found a clear trend:
Out of all the special elections with typical Democrat vs. Republican dynamics, Democrats have overperformed the 2016 presidential margin by more than 10 points in 25 of them. Republicans have overperformed by more than 10 points in just four — but one of those was actually a Democratic flip! On average, Democrats are doing about 13 points better than Hillary Clinton.
The Virginia results in November were equally impressive, with gubernatorial candidate Ralph Northam winning by the largest margin of any Democrat since 1985. And the Donkey Party’s shocking Virginia state legislative gains, heavily concentrated in suburban communities, showed that the disdain for Donald Trump among college-educated white voters was rubbing off on down-ballot Republicans.
Still, all these positive indicators for Democrats don’t translate proportionately to gained House seats, even if they persist in 2018. The generic ballot, for example, simply predicts the national House popular vote, not seats gained, and it’s not at all clear how big a margin in the popular vote Democrats will need in 2018 to win back the House. Harry Enten explained the problem back in February:
[I] f Democrats win the national House vote by a margin in the low- to mid-single digits, that may not be enough to take back the House. The median congressional district was 5.5 percentage points more Republican-leaning in the presidential race than the nation as a whole in 2016, meaning Democrats are essentially spotting the GOP 5.5 points in the battle for control of the House. And even that may be underestimating Republicans ability to win a majority of seats without a majority of the vote. Since 2012 (or when most states instituted the current House district lines), Republicans have won, on average, 51 percent of the two-party House vote and 55 percent of House seats. If that difference holds for 2018, Democrats would need to win the House popular vote by about 8 percentage points to win half the House seats.
Incumbency and redistricting are the big institutional reasons the GOP upholds its House majority, despite likely Democratic margins in the overall popular vote. But as the Cook Political Report’s Amy Walter notes, those advantages may be eroding as the party and its president grow less popular:
In the most recent October survey, [NBC News] found that Republicans had a six-point advantage in GOP-held seats (R+6), while Democrats had a 29 point advantage in seats they hold (D+29). What’s significant—or what NBC/Wall Street Journal pollster Bill McInturff called a “flashing yellow light,” was that the GOP advantage in seats they already hold dropped eight points from September to October—from R+14 to R+5. It also stands in stark contrast to the average generic advantage Republicans had in seats they held in the most recent mid-term elections (R+15 in 2010 and R+18 in 2014).
The pace of House Republican retirements has picked up recently as well, and with incumbency worth an estimated seven points as compared to similar races with non-incumbents, that could be a really big deal. But most of the 29 announced GOP retirements are for Members in non-competitive districts. According to Cook Political Report, there are at present just six competitive House seats being vacated by retiring Republicans, along with three such Democratic seats. A few more, particularly in the 23 certified Trump-resistant districts carried by Hillary Clinton last year, could make a big difference. Another factor that could erode the usual advantages of incumbency is the unusually large number of Democratic challengers who are raising serious early money.
Looking more closely at individual districts, New York has identified 40 races to watch next year. Of the 32 in districts currently held by Republicans, the Cook Political Report (which is very conservative about projecting upsets) lists 12 as toss-ups, another 18 as leaning Republican, and two as likely Republican. In the eight Democratic-held districts to watch, Cook calls three toss-ups and the other five as races leaning Democratic.
If a Democratic wave begins to form, you could see all the toss-ups moving Democratic and a number of the Lean Republican races moving into very vulnerable territory (along with some of the 25 Likely Republican districts becoming competitive). In 2010, the last wave election, the Cook Political Report showed the competitive districts literally doubling between November 2009 and November 2010, with the number of vulnerable Democratic seats jumping from 37 to 91. One thing to watch right in the very near future is whether House Republicans pass a tax bill that kills the state and local tax deduction — hammering upper-middle-class itemizers in California, New Jersey, and New York — and how many of the nine vulnerable GOP incumbents from those states vote for it. As the actual midterm election year approaches over the holidays, it could be a perilous time for House Republicans.
In the end, control of the House would be of great value to Democrats, given the majority’s power in that chamber to control what comes to the floor and what gets attention. It would signal a formal end to the GOP’s window of opportunity in enjoying a federal government “trifecta.” But even if Democrats simply make significant gains short of a majority, shrinking the GOP margin could have a major practical effect. As we’ve seen in the Senate this year, the Republican Party is not unified enough to pass legislation with much of a margin for error.