AS MAGA HEARS it, the sound of the border is the trill of gunfire and the cry of trafficking victims. In reality, it is a lot more heartwarming: the toot of the trumpet, the strum of the guitarrón, the yelp of the grito, the stomp of patent-leather boots. It is the sound of a bunch of Texan high-school students playing mariachi, for love and for course credit.