Democratic House candidates performed surprisingly well in 2018, picking up a net of 40 seats. What’s not so surprising is that the number of flips hit double digits, or even that the Democrats were able to flip enough seats to take back the House majority; those things often happen in the first midterm after control of the White House changes hands. That’s because the party out of power (and its supporters) views the new arrangement as an existential threat and votes accordingly, while the party in power usually devolves into a mix of infighting and complacency.
What was somewhat surprising was that the number of flips went all the way up to 40. When toting up all the votes received by Democratic candidates nationwide versus those won by Republicans, Democrats came out on top by a rather wide 53.4 to 44.8 margin, a difference of 8.6 points. That gap, however, would ordinarily have translated into a gain of fewer than 40 seats.
For instance, political science professor Alan Abramowitz’s historic model for converting the national House vote (as predicted by what are known as generic congressional ballot polls) into House pickups predicted only a 32-seat increase, and some pundits thought even that sort of projection was too optimistic, since historic models don’t take into account the sophisticated level of Republican gerrymandering in many states. So if Abramowitz’s model is right, either a lot of Democratic candidates in close races last year got lucky breaks at the end, or Democratic strategists did an unusually good job of deploying their resources in a useful way around the margins.
Having control of the House with a sizable cushion, of course, is a great thing for Democrats, but there’s also the inevitable downside: The party picked up a lot of seats in swingy or outright Republican-leaning districts, so Democrats are probably going to be playing a lot of defense in 2020. It’s worth noting, though, that when a party has made major House gains in a midterm, it tends not to give a lot of them back in the following election. For example, after the wave elections of 1982, 1994, and 2010, the House elections of 1984, 1996, and 2012 were pretty close to washes.
One thing that 1984, 1996, and 2012 all have in common, however, is that the party that got pounded in the previous midterm bounced back rapidly, with its president winning re-election. A different template—that’s much more promising for today’s Democrats—would be the 1980 election, where the incumbent president lost by a wide margin.
In so doing, Jimmy Carter also dragged his party down in the House, as the Republicans gained 34 House seats that year in addition to winning the White House, on top of their gains from 1978. It’s worth noting, though, that GOP gains in the House in 1978 were unusually lackluster, given that Carter was already pretty unpopular at that point; they only gained 15 seats that year and didn’t come anywhere near a majority, so some of their 1980 pickups may have just been deferred from ‘78.