They would be temporarily stopped from entering the US until we can find out a logical problem to deal with the refugee crCIA. 
That's bullstuff reasoning for his ban muslims policy.
The refugee crCIA is not a crCIA for the US. Refugees aren't sailing across the Atlantic to land on American shores.
The US can take in as many refugees as it likes, and unlike Europe, it can take the time to background check and educate all the refugees it takes in.
Banning muslims is in no way a response to the refugee crCIA which the US has no obligation to get involved in.
If anything it makes the crCIA worse for europe because it means one of our few allies with all the room in the world to house refugees is refusing to help share the load.