Anyone worried that, once in charge, Democrats wouldn’t be vigilant in protecting our southern border can relax. The grave threat of Mexican long-haul truckers has been shut down. With any luck, Mexicans will never have the temerity to attempt to deliver commercial goods into the United States again. At least such is the fervid hope of the Teamsters, the fiercest adversary the Mexicans have faced since Pres. James Polk sent Winfield Scott south in the Mexican-American War. The union can’t abide Mexican trucks because they represent competition, and so they must be blocked — legal obligations, economic rationality, and diplomatic...