People are beginning to talk about the 2018 midterm elections and I’ve heard a few people repeat the myth that Republicans reliably do well in midterms, or at least better than they do in general election years.
This is only true if the president is a democrat. When the president is a republican, the GOP does poorly during midterm years. By contrast, when it is a general election year the GOP does better when the president is a republican and worse when the president is a democrat.
To show that this is so, I analyzed how the average change in seat count for Republican in the house varied depending on whether the election was a midterm, and whether the president was a republican. The data I used for for each US election between the years of 1946 and 2016, a 70 year period.
As can be seen, these numbers don’t suggest that republicans should be confident about 2018 simply because it is a midterm. If anything, they should be nervous because there is a republican president.