As set forth in Article I of the US Constitution, seats in the US House of Representatives will be assigned to the states based on counts of the population obtained through the decennial census. The Constitution is silent regarding the definition of the apportionment population. Given current partisan debates regarding immigration and citizenship questions on the 2020 Census, in this article we ask how the 2020 apportionment of House seats might change if the apportionment definition is altered via aspects of citizenship and immigration. We show, first, that historical immigration has significantly favored states that, based on recent election results, tend Democratic. This goes a long way towards explaining the deep political schism on immigration. A second scenario indicates that excluding non-citizens from the apportionment population would have a minor effect on apportionment from the Republican vs. Democratic-leaning state perspective. Most striking and timely, removing undocumented immigrants from the apportionment population would have only trivial effects on the partisan political alignment of the US House of Representatives. There would be little to no change in the overall number of seats allocated to Republican- or Democratic-trending states. The addition of a citizenship question on the 2020 Census, which will likely increase the population undercount, will be unlikely to significantly alter the political strength of either party in the US House of Representatives.
Published in a peer-reviewed journal of the Population Council.