By Nathaniel Rakich of FiveThirtyEight
Turnout can vary pretty dramatically among congressional districts, which is one reason that the partisan breakdown of seats in the House doesn’t necessarily match the results of the national popular vote. The way this usually unfolds in practice, at least in midterms, is that fewer votes are cast in Democratic districts than in Republican ones, which works in the Democrats’ favor.
States lack reliable data on how many eligible voters there are. That’s why some believe that the Trump administration’s push to add a question about citizenship to the 2020 Census may be an entree to redrawing districts based on the number of eligible voters.
So keep an eye on this seemingly overlooked distinction; it could emerge as the major fight in the next round of redistricting.