First, he is a xenophobe.
Second, he is just using xenophobia to score political points.
See: Mexicans-as-rapists, constant immigration fearmongering, MS-13 obsession, Muslim ban (not a ban!), decreased acceptance of refugees, "shithole countries," and most of all, of course, family separation as a method of deterring immigration.
That is off the top of my head in about 13 seconds.