Some states have made the drug legal for medical purposes; others have removed jail sentences for carrying small amounts; and some let adults 21 and older use it for any reason.
The dissenting circus owners have repeatedly complained the law has not been accompanied by a programme to assist and shelter all animals that can no longer live and work in circuses.
It means more state troopers, cameras and a spy plane to patrol Texas' 1,200-mile border with Mexico.