Have you heard of the Tren de Aragua, a Venezuelan criminal gang? Maybe not, but this is “the little engine that could” that may bring your quiet American neighborhood some dangerous young men with little to contribute and even less to lose. Joseph Humire, an expert on Latin American security, calls the Tren “the fastest-growing transnational criminal organization in the world.” Last year, the Tren de Aragua didn’t even make the Border Patrol’s “Nationwide Apprehensions by Gang Affiliation,” an alphabetical list of 50 Central and South American gangs invading the United States—from the Angelino Heights Sureno 13 to the Zetas....