Well...they certainly do have the right to admit who they choose, but one of the essential components of democracy going back to the signing of the Magna Carta is an expectation that everyone will be treated equally under the law.  This step by Trump is contrary to the very ideals espoused by the USA in their constitution.  Still...if there was a compelling reason for such a ban then it could be justified.  So what reasons are there?  The US vetting system for refugees is far and away the most comprehensive in the world.   There has never been an attack in the USA by a refugee.  So what are the reasons for the ban?  We can speculate that they are solely to pander to Trump's political base of low educated white males who fear competition for their social benefits.   In the past he's proposed a ban on Muslims "until we can figure this thing out."  What thing?  What's to figure?