Donald Trump began his presidential campaign with a commentary about immigration that jolted the race and indeed the very idea of what was advisable or acceptable for a candidate to say.

“The U.S.,” he declared in June 2015, “has become a dumping ground for everyone else’s problems. … When Mexico sends its people, they’re not sending their best. … They’re sending people that have lots of problems, and they’re bringing those problems with us. They’re bringing drugs. They’re bringing crime. They’re rapists. … They’re sending us not the right people.”