The Washington Metropolitan Police Department (MPD) inquiry into whether NBC’s David Gregory possession on national TV of an illegal 30-round “high-capacity” magazine has been ongoing for three weeks. Meanwhile, U.S. Army veteran James Brinkley is still grappling with the fallout from his arrest last year on the same charge. Mr. Brinkley’s story is just one example of at least 105 individuals who, unlike Mr. Gregory, were arrested in 2012 for having a magazine that can hold more than 10 rounds. On Sept. 8, Mr. Brinkley says he intended to drop his wife and young children at the White House for...