Billy "Saxophone" Clinton may have passed this law in 97, but the policy wasn't enforced it until Trump found it. There are thousands of laws on the books that are not enforced or strictly enforced because of policy. Trumps people found this law and decided to enforce it as a bargaining chip for his border wall. Honestly, his supporters are so stupid and he is such a liar, he could just tell them the Wall was built and they would just believe him.