Javier Milei’s triumph in the first round of the Argentine elections last year—the first of three that make up our tortuous process of electing a president—provoked not just shock, but confusion. Immediately, WhatsApp threads were bursting with different versions of the same question: Was he “far right”? Or was he something more bizarre—the first libertarian candidate in the world with a chance to win? The question was—and is—far from foolish. Milei presented himself as a central part of a new right-wing international, expressing solidarity with world leaders like Donald Trump and Brazil’s Jair Bolsonaro. Everyone was happy then: The global...