Taylor Swift has not endorsed anyone in this year’s presidential race. But her army of fans isn’t waiting for her. Swifties know which way she leans. Swift, currently traveling in Europe with her mammoth Eras Tour, endorsed Joe Biden and Kamala Harris in 2020. Since Sunday, when Biden stepped down from his reelection campaign and Harris became the presumptive Democratic nominee, Swifties have flooded social media supporting Harris, enchanted by the prospect of the first female president. If the mammoth success of Swift’s tour has demonstrated anything, it’s this: When millions of Swifties mobilize, get out of their way. And...