I’ve read that some have suggested that banning muslims would be unconstitutional. Instead of fighting that battle, all a president has to do is halt immigration from certain countries or regions.
https://history.state.gov/milestones/1921-1936/immigration-act
We had restricted immigration from 1924 to 1965.
When you consider that the Nice maniac was a French citizen, it isn’t enough to let ANYONE in the US based on their country of citizenship. There has to be excellent vetting of everyone granted any form of residency in the US (including students)