Reapportionment

Census fun:

By that new count, Texas will gain four new seats, Florida will gain two, while New York and Ohio each lose two. Fourteen other states gained or lost one seat. The gainers included Arizona, Georgia, South Carolina, Utah and Nevada, and the losers included Illinois, Massachusetts, New Jersey and Louisiana.

The superficial analysis is that this is good for Republicans. More sophisticated analysis, in fact, also indicates that it's good for Republicans. Something else to note is that the seat-losing states generally aren't actually losing population it's just that around 100 years ago we decided to stop increasing the size of the House of Representatives no matter how big the national population grew.