Trump discovered that president of a country is not same a president of a private business. Found out at age 70. Totally amazing.

He discovered that, while banning individuals for legal reasons is appropriate for all countries, blanket banning of all nationals from entire countries is illegal under international laws which are enshrined in treaties the U.S. Congress signed. But countries who did same in response to such an illegal ban is in fact legal. 

He will discover that imposing 20% blanket tariff is illegal under both WTO and NAFTA and will be struck down by the court. But the exact retaliation is legal. 

And now I come to the real reason why Trump is in such a hurry to ban from the 7 countries. The Obama administration have bombed the 7 countries resulting in 25,000 deaths according to independent observers. The CIA estimated that there are now enough anger for them to stage another 9/11 and have detected signs. It urge Trump to blanket ban travels to check any such plans.