Jeb Bush, the man who would be frontrunner, was as surprised as anybody when Donald Trump jumped into the 2016 presidential race in June. His instinctive first reaction was to hold his tongue, and his advisers agreed the best option was to keep his distance from an interloper who wanted to drag him into a reality-show shouting match. Bush stayed strategically silent even when Trump delivered his infamous crack that some Mexican immigrants were “rapists.” It wasn’t easy, considering Bush speaks nearly flawless Spanish, backs comprehensive immigration reform and is married to the former Columba Garnica de Gallo of Leon,...