Superior enthusiasm, an unpopular GOP president, and now an advantage in early congressional polling: All these are assets for the donkey party going into the midterms. Photo-Illustration: Daily Intelligencer; Photos: Getty Images

To the gradually but steadily increasing body of evidence that Democrats are likely to have a solid performance in the 2018 midterm elections comes another factor: the so-called “generic congressional ballot,” which means polling of which party voters are likely to prefer in upcoming U.S. House elections.

FiveThirtyEight’s Harry Enten notes that in generic congressional balloting Democrats are in the best position at this early stage of the midterm election cycle of any opposition party dating all the way back to 1942. They currently lead the GOP by a 45 percent to 40 percent margin in the polling averages.

Democrats are in a historically great position according to the generic ballot. Typically, at this point in a midterm cycle — the first half of the year after the preceding presidential election — the party in control of the House is fairly popular. Most likely, they did at least OK in the last election (they still control the House, after all) and they simply haven’t had enough time to upset the electorate too much. Republicans in 2017, though, are one of the exceptions to the rule.

As Enten observes, one of the other rare moments when the party controlling the House looked to be in relatively bad shape the year before midterms was in 2013, and Republicans rebounded to do very well in 2014. They did not, however, have the current GOP Congress’s handicap of being the White House party.

[H]ere’s the problem for the GOP: Midterms are almost always about the president. Voting for Congress in midterm years is essentially just a mechanism for passing judgment on the White House. In 2018, unlike 2014, the House and presidency will be controlled by the same party. And when we look at the generic ballot numbers this early in the cycle while also accounting for who holds the White House, the generic ballot has forecasted midterm House results fairly well.

According to Enten, the historical record suggests the Democrats’ current 5-point margin in the generic congressional ballot should — all other things being equal — swell to about 8 points by November of 2018. That’s near, if not equal to, the size of the national popular-vote margin they will need to regain control of the House, given the obstacles they face thanks to Republican gerrymandering and superior vote distribution.

None of these calculations, however, fully take into account the phenomenon of a president as unpopular as Donald Trump is at present. One would figure his unpopularity, if it is sustained, will be a further drag on GOP performance in 2018. The other way to look at it, though, is that the current generic ballot numbers already factor in an unpopular GOP president, and since his numbers may not go much lower (given his solid and hard-to-disappoint base), perhaps Republicans won’t suffer the usual slide going into the midterms.

Any way you slice it, though, it is not a good sign for Republicans that all the indicators for 2018 look negative, with the main consolation being that they may not get much worse. If they do, it could be time for a grand old disaster.