James, from my experience I'd say you are right about many of the international students here, but not, however, "invariably."  Some are just hanging on with the little their families can spare as well as their teaching assistantships if they are lucky enough to have one.  Thus enrollment has fluctuated somewhat over the years depending on the strength of the dollar. 

 However, I agree with you that at this moment the major  cause of the decline is more America's rising insularity, negativism towards "outsiders."  There seems to be some resentment  locally towards seeing international  students around the campus in "flashy sports cars."
This reminds me of my wonderful army days in Lubeck Germany 1959-61, a time when the  dollar was worth four marks and even us GIs lived like kings.  There probably was some local resentment towards our affluence, though mostly they were friendly to us.
Now I wish my current president were more friendly to Germany's current leader.