Donald Trump Saturday moved his arena from a large outdoor field to, in his words, “a small arena,” and then blamed Vice President Kamala Harris for the change. Trump spoke at an indoor rally in Prairie du Chien, Wisconsin, where at one point he called Harris “a mentally disabled person.” The former president had originally slated a rally at a Wisconsin airport on Saturday, but those plans were tossed out when the Secret Service stated it did not have the manpower on the same weekend that foreign dignitaries were flooding New York City for the annual meeting of the United Nations General Assem…