Former President Donald J. Trump, who has notably harbored a grudge against the pop music megastar Taylor Swift, set the internet ablaze on Sunday when he shared social media posts suggesting that she had endorsed him and that her fans could help him win the November election. In a post on his social media site, Truth Social, Mr. Trump drew attention to a group of images that were created using artificial intelligence. One showed Ms. Swift dressed up as Uncle Sam with the headline: “Taylor...