BUENOS AIRES, Argentina — Javier Milei, a far-right libertarian economist, has stayed aloft in Argentina’s presidential campaign on the wings of the youth vote. To win the runoff election this month, he will need to hold on to that key demographic, pollsters say. But now, a major hurdle stands in his way: Swifties. Squadrons of Argentine fans of pop star Taylor Swift have gotten political. They have trained their online sights on Milei and his rising libertarian party, framing them as a danger t