What determines who is up for re-election in the Texas Senate every two years?

In the Texas Senate, the structure is designed to ensure continuity while allowing for periodic renewal. Senators serve staggered terms, with half of the Senate seats up for election every two years. This rotating system is established to prevent complete turnover in the Senate at any given election cycle, thereby maintaining some level of institutional knowledge and stability within the legislative body.

To achieve this, Texas Senate elections are organized such that approximately half of the 31 senators are elected every two years. This means that as terms are staggered rather than synchronized, it creates a predictability regarding which positions will be contested in a given election cycle. Consequently, the rotating system effectively determines who is up for re-election, ensuring that the Senate does not change dramatically in membership at any point.