Rules of thumb are just rules of thumb, which means they aren’t “rules” at all, but tendencies based on how the experience of the past might help picture the future.
One such rule of thumb that has been quite powerful in predicting the future of midterm congressional elections is that the party that controls the White House tends to lose ground in the midterm. The tendency has been undeniably true much more often than not.
And, in the current situation, with Democrat Joe Biden in the White House and Democrats clinging to very small majority in the U.S. House and the barest imaginable control of the U.S. Senate, history suggests that Republicans will likely take majority control of both or certainly at least one of the houses of Congress in January of 2023.
Again, It’s just a rule of thumb. But it may have more than the usual predictive power based on one more oft-cited factor: retirements.
As of now, according to this recent Washington Post overview, 30 House Democrats have announced that they will retire at the end of the current session of Congress, compared with just 17 House Republicans.
As a general matter, open seats (meaning no incumbent) make it more likely for the seat to change hands from one party to the other, though you have to look at each of the seats that will be open in November to decide how many of those will turn into pickup opportunities for the out party. Some of those retiring Democrats are in seats that will be tough for any Republican to win.
But others will be highly competitive without an incumbent Democrat running, and 30-17 is a significant margin. Without going district by district, it’s likely that a reading of the political tea leaves played a role in some of those House incumbents’ decisions — that this would be a good time to retire.
In short, while Joe Biden has had a very small partisan advantage during the first half of his term, it will quite likely be even smaller to non-existent in the 2023-24 biennium.