It was the ideal audience for Donald Trump. American Airlines center was packed with 20,000 enthralled Texans who seemed to hang on every word of boast, harangue, and self-aggrandizement that passed through Trump’s lips. They whooped and hollered through 90 minutes of Trump speech-making. In scattered and rather loose references to issues, Trump skillfully intermixed attributes of puerile boasting about his skills, mocking his opponents and their cluelessness, and lionizing his “oft-demonstrated” business skills. The biggest winner was his condemnation of American immigration policy while characterizing all “illegals” as leaving a large swatch of murder, rape, and pillage in their...