Jonathan Pie explains it

[Clodfobble]

One admissions officer from a medical school reported that they have been instructed to toss out all applications from those seven countries, regardless of anything else, because they cannot guarantee that the 90 days will not be extended.

When you're a politician, you understand that the hysteria is the act, just like the economy runs on belief and not reality. If everyone goes apeshit, it doesn't matter if he never intended for it to happen--part of his job is to predict that it would happen.