> ... DHS, at every border crossing and airport ...
I think you misunderstand - certain travellers to The Land of the Free will, under Gen. Kelly's plans, have to cough up their passwords before travelling, e.g. when applying for a visa, or an ESTA.
Others have pointed out that disclosing passwords is uniformly a breach of Terms and Conditions, and presumably it will harm your application for the visa if you change the password during the period when DHS is getting around to logging in with the extorted credentials and having a rummage. At a stroke, Gen. Kelly sacrifices the security of *all* his target travellers, for the sake of an outside chance of identifying the tiny fraction of them that might be undesirable.
However, it is clear how the current administration views travellers from certain (coincidentally Muslim) countries. They're all undesirable. If the criteria really did have to do with countries with a history of terrorism, then the Irish nations would be on the list too, wouldn't they?