When the first U.S. House of Representatives met in 1789 it had 65 members. The size of the House then expanded steadily over time as the population grew and new states were admitted, up until the Apportionment Act of 1911. That law set the size of the House at 433 members but also made a provision to add two new seats upon the admission of New Mexico and Arizona to the union.

Then came the controversial 1920 Census, after which Congress refused to reapportion the House at all in a huge breach of constitutional norms.1

But a new Reapportionment Act did happen in 1929, and after that, we went back to the routine of changing up House apportionment after each Census to account for shifts in the population. But we didn’t go back to the old habit of changing the overall number of seats, which instead stayed fixed at 435. Even the admission of Alaska and Hawaii didn’t lead to the creation of new seats for new states the way it had for New Mexico and Arizona.

People sometimes talk about this a…