The Immigration and Nationality Act of 1952 grants “the President broad authority to bar or impose conditions upon the entry of aliens.”
U.S. Code § 1182
Inadmissible aliens: “Whenever the President finds that the entry of any aliens or of any class of aliens into the United States would be detrimental to the interests of the United States, he may by proclamation, and for such period as he shall deem necessary, suspend the entry of all aliens or any class of aliens as immigrants or nonimmigrants, or impose on the entry of aliens any restrictions he may deem to be appropriate.”
The seven countries
Three of them — Iran, Sudan and Syria — comprise the State Department’s list of state sponsors of terrorism. The other four — Iraq, Libya, Somalia and Yemen — are designated “terrorist safe havens” by the State Department.
Total ban on Syrians
Islamic State militant group that organizes terrorist acts around the world operates in Syria, which has been devastated by a nearly six-year-long civil war. About 11 million Syrians — half the population — have been displaced.