There are 435 congressional seats among the fifty states and there are divided up after each U.S. Census. After the 2020 Census, Pennsylvania is projected to lose yet another seat.
This means in a few years the state legislature will have to eliminate a district and PA will have one less electoral vote in presidential elections (electoral votes are based on the number of congressional Representatives and Senators a state has).
Pennsylvania is used to this phenomenon by now, though, as the state hasn’t survived a Census without losing at least one seat since 1920. Overall, there has been a long-term trend of Northeastern and Midwestern states losing population to the South and West of the country.
For example UNC predicts that alongside PA; Illinois, Michigan, Minnesota, New York, Ohio, Rhode Island and West Virginia will also all lose a seat.
Arizona, California, Colorado and Oregon are considered possibilities to gain another seat while Florida, North Carolina and Virginia are considered certainties. UNC also projects that Texas will gain two seats.
Based on the 2012 electoral map, red states would gain five additional electoral votes under this scenario.