Whatever the government does to protect against terrorism must be done constitutionally. There are examples out there— strict gun control and control of explosives, and electronic eavesdropping would help control terrorists, but the constitution prohibits most of those things. Even bans against sanctuary cities would fail against strict constitutional tests as the late Supreme Justice Scalia pointed out in his opinion rejecting the idea that the Federal government could force States to enforce federal gun control laws. This also goes for a travel ban. Some form of control can be done constitutionally— like the one we already have to which we can add even more. This latest attempt may now go back to the Federal District courts, and to the Federal Appeals Courts before it it heard by the US Supreme Court.— do not be surprised.