The State Border Defense Act would allow state and local law enforcement officers in any state to enforce federal immigration laws that prohibit unlawful entry into the United States, effectively overturning a 2012 Supreme Court decision that limited states' authority in this area. The bill would also permit California, Arizona, New Mexico, and Texas to construct barriers on federal lands along the southern border to prevent illegal entry, provided these barriers do not interfere with Border Patrol operations or lawful movement and commerce. Additionally, the legislation authorizes state prosecutors to bring charges for federal immigration violations in federal courts. The bill does not contain specific funding allocations or implementation timelines. If enacted, this legislation would significantly expand state and local government involvement in enforcing federal immigration law and managing border security infrastructure.