As of this writing the infamous Presidential executive order banning entry into the U.S. from seven predominantly Muslim countries has yet to get a final judicial ruling. But whether it succeeds or fails, its main purpose will have been achieved: to instill fear in those deemed undesirable by Trump, Bannon, & Co.
From that perspective, it’s all the worse if the ban is eventually determined to be constitutional. You can do more than just scare helpless undesirables, you can lawfully inflict pain on them. The undesirables could be any group—Muslims, Mexicans, Arabs, etc.—for which you can find some pretext to justify barring them from entry, throwing them out, or jailing them.
Much was made by Republicans that it was only a “temporary” ban. But of course once you have a “temporary” ban, what’s to keep it from being extended in the name of national security? The point is not about temporariness or permanence, the point is about power and intimidation.