After Donald Trump’s cringe-worthy interaction with school-aged children in the Oval Office on Tuesday to promote his administration’s revival of the Presidential Fitness Test, I got a phone call from an aging former Republican officeholder who said seeing Trump interact with kids was like watching Richard Nixon’s “Checkers Speech.” He was referring to a televised address that Nixon, then a California senator and Dwight Eisenhower’s running mate, gave in the heat of the 1952 presidential campaign in which he exploited his eldest daughter to rebut serious charges of using a secret campaign fund for personal use. Part of the accusation was aimed at a cocker spaniel the Nixons were given by a supporter that his six-year-old daughter Tricia had named Checkers. The speech was exploitative, but not demeaning, and the public forgave Nixon.  What Trump did was much worse. As a grandfather and a father, let me say it bluntly: How the president of the United States spoke to children that day was wrong. He didn’t talk about puppies — he discussed mass shootings, people …