“Mexico First” has been the open, avowed policy of the government of Mexico for a generation, and Mexico expects its former residents to be loyal to Mexico for the next 200 years. Yet, when Donald Trump calls for an “America First” foreign policy, as he did in a speech this past week, he is denounced by pundits and the national security establishment for “nativism” and “demagoguery,” as if that policy is a novel and radical idea. Well, not in Mexico. I know that for a fact because I had it explained to me in Mexico City back in 2001 by...