Our Best Tool For Predicting Midterm Elections Works In Presidential Years Too

If you followed polls of the generic congressional ballot, you knew as early as summer 2017 that signs pointed to a wave election for Democrats in 2018. Now, for your prognosticating pleasure, the FiveThirtyEight generic ballot tracker is back to help you track the battle for the U.S. House in 2020. The congressional generic ballot question asks voters which party or which party’s candidate they’d support for Congress (usually as opposed to the name of the specific candidate they plan to support).¹ And as of midday Wednesday, Democrats held a 6.2-point lead over Republicans — a solid advantage but still smaller than the 8.7-point lead they held in our polling average on Election Day 2018.² This jibes with other early signs that suggest that while Democratic enthusiasm has ebbed a bit since last year, the political environment still favors Democrats.

A 2017 analysis by erstwhile FiveThirtyEighter Harry Enten found that the generic congressional ballot is one of the most accurate predictors of who will get the most votes for Congress in a midterm election. I wondered whether the same could be said for generic ballot polls in presidential election years. Borrowing from Harry’s methodology, I conducted a similar analysis for recent presidential election years and found that their generic ballot polling is just as predictive. Specifically, for presidential election cycles starting with 1996, I compared either Gallup’s final generic-ballot poll of the cycle³ or RealClearPolitics’s final polling average⁴ with the House national popular-vote margin and found that the final polling missed by an average of 2 percentage points.⁵ The same analysis for midterm election cycles starting with 1994 found that the final polling in those cycles missed by an average of 3 percentage points.⁶

Harry also found that even early generic-ballot polls, more than a year before a midterm election, have some predictive power. My analysis found the same for early generic-ballot polls in presidential cycles like 2020. Basically, although polls can certainly evolve over time, generic ballot polls have historically proved pretty stable.

The table below compares the national House popular vote in presidential cycles since 1996 with an average of pollster averages⁷ that I calculated using all the polls I could find from between January and June of the year before the election. And as you can see, it reveals a decent relationship between a party’s performance in early generic-ballot polls and its ultimate performance at the ballot box. That is, the national House popular vote in presidential cycles has usually wound up within a few points of those early polls. In most presidential cycles, the two parties were neck and neck in early generic-ballot polls, as they were in the eventual congressional elections (as measured by the popular vote). The lone exception is 2008, which was a Democratic wave year — something the early generic-ballot polls correctly predicted.

In summary, generic congressional ballot polls — even early ones — are good measures of the national mood. And because the national mood affects not only congressional elections, but also presidential ones, that means generic ballot polling might provide a back door for approximating presidential election results too. As you can see in the table below, final generic-ballot polling — and to a lesser extent early generic-ballot polling — has come pretty close to the results of the national popular vote for president as well as for House since 2000. That’s pretty good, considering these polls are measuring elections for an entirely different branch of government, although it’s worth noting that even a polling error of 3 or 5 points can change the outcome if the race is close.

It’s yet another demonstration of how partisanship is the dominant force in today’s politics; these days, people overwhelmingly vote for the same party up and down the ticket. Congressional vote preferences may not drive the results of the presidential race (it’s more likely the other way around), but the former still reflect the latter. And if early generic-ballot polls are, as they seem to be, mildly predictive, then the fact that Democrats currently lead them by 6.2 points is a bad sign for President Trump. It suggests that the national political environment is still blue, and given how closely the House and presidential popular votes have lined up this century, that’s an important thing to keep in mind for the 2020 presidential election.

Check out all the polls we’ve been collecting ahead of the 2020 elections.