For the past decade, Republicans have enjoyed a tremendous structural advantage in the House of Representatives. And the idea of them losing it in the near future was virtually unthinkable until last year's wave swept them into the minority.
In 2010, the GOP won control of the redistricting pen throughout the Midwest and most of the South, allowing them to concoct aggressive partisan gerrymanders that let them win a majority of seats even as they lost the House popular vote. Moreover, the geographic spread of Republican voters benefits them even without gerrymandering — a combination of natural migration patterns and generations of racist, classist, and discriminatory housing policy has resulted in an inefficient distribution of Democratic voters. They tend to be "packed" into dense, overwhelmingly blue urban districts while Republican voters are spread out more evenly across suburban and rural ones, making it all too easy for a congressional map to favor the latter.
It would be easy to think, then, that the gigantic blue wave that swept House Democrats into power in 2018 will just be a brief interlude in the GOP's monolithic dominance. After all, Democrats followed up their previous back-to-back wave elections in 2006 and 2008 by losing 64 seats and their majority in 2010. So it's not out of the question that Republicans could reclaim the House in 2020, as some commentators have suggested could happen.
But will they? In fact, there are several reasons to suppose that Republicans will be fighting an uphill battle to retake the lower chamber.
To begin with, the type of House seats Democrats flipped in 2018 are broadly different from those they flipped in the previous Democratic waves of 2006 and 2008. In those elections, Democrats built a broad-based but fragile majority with conservative, rural seats — they held a majority of the seats in Mississippi and Arkansas, a number of rural seats in Indiana, Ohio, and Tennessee, the at-large districts in North and South Dakota, and even a seat in Idaho — all places demographically and culturally trending away from them. By contrast, most of the seats Democrats picked up in 2018 were in suburban districts swinging towards them — even many of the most conservative seats whey won, like in South Carolina, Oklahoma, and Utah, are anchored by diversifying suburban communities. It will be hard for Republicans to reclaim these areas for the same reason it was hard for Democrats to make up the territory lost in 2010.
Then there is the fact that the GOP's structural advantage itself is weakening. Gerrymanders tend to become less effective over time as voters move and populations shift. Additionally, some of the 2010 gerrymanders--in Pennsylvania and Florida--were struck down outright by the courts, and some others, like North Carolina's, could be struck down before the next election.
In addition to those dynamics, Republicans are blowing new holes in the map as members announce their retirement in competitive seats. Rep. Rob Woodall (R-GA) has created a frantic scramble by announcing his retirement, after only holding onto his seat in 2018 by a fraction of a percent. And Rep. Susan Brooks (R-IN) — the National Republican Congressional Committee's recruitment chair — recently announced her own departure from a rapidly diversifying suburban district. Retirements played a huge rule in Republicans losing the House in the first place, and tend to precede bad election years for the party in question.
All of this would be comfortably difficult enough for the NRCC if they had competent leadership. But they don't.
From the outset of taking the job, NRCC chairman Tom Emmer (R-MN) denied President Donald Trump was a liability for House candidates in 2018 or that the GOP in any way needs to change its message in the suburbs. Their communications staff are essentially a gang of trolls, at one point harassing Democratic freshman Rep. Lucy McBath's elderly relatives through the mail to try to prove she doesn't live in Georgia. Communications Director Chris Pack is laughably inept, recently putting out an email blasting Democrats for a proposed congressional pay raise that Republican leaders themselves negotiated. Meanwhile, NRCC leadership is fighting with several key House members for not paying their dues as they decide whether to run for Senate, including Reps. Gary Palmer (R-AL), Mark Walker (R-NC), and Liz Cheney (R-WY), who in turn accuse Emmer of double-counting funds to make it look like the NRCC has more money than it does, adding to both money problems and intraparty tensions.
2020 is not going to be a cakewalk for Democrats. The cycle will be dominated by the all-consuming task of defeating Trump, and incumbents are hard to dislodge even when they are unpopular. Retaking the Senate will be extremely difficult, as most of the seats in play this cycle are in deep red states. And Democrats have to fight out a series of high-stakes state and local elections that will decide who controls redistricting for the next decade.
The one bright spot for Democrats, then, is that for once, holding onto the House majority should be the easy part.