As the U.S. puts up barriers to would-be migrants coming across the southern border, Latin America is undergoing a sharp political shift. Politicians from Peru to Colombia are copying Donald Trump’s style and are themselves launching crusades against migrants and the left. Disillusionment with socialism and fears of ending up like Venezuelan leader Nicolás Maduro — i.e., captured by U.S. special forces — have turned Latin American societies riven by class hatred into a showcase for what may be Trumpism’s only foreign-policy triumph to date.