Robert Crimo Jr.’s guilty plea to reckless conduct for helping his son obtain authorization to own firearms three years before Robert Crimo III allegedly opened fire on Highland Park, Illinois, paradegoers should be a wake-up call to everyone: If you hear or see things about potential violence, you must alert the authorities. And if you do things that could potentially enable it, you will face legal consequences. Crimo Jr. agreed earlier this month to plead guilty and was sentenced to 60 days in jail and two years on probation. He also will have to complete 100 hours of community service. Pros...