Mary L. Trump, President Trump’s niece, plans to publish a tell-all family memoir next week, describing how a decades long history of darkness, dysfunction and brutality turned her uncle into a reckless leader who, according to her publisher, Simon & Schuster, “now threatens the world’s health, economic security and social fabric.” The book, “Too Much and Never Enough: How My Family Created the World’s Most Dangerous Man,” depicts a multigenerational saga of greed, betrayal and internecine tension and seeks to explain how President Trump’s position in one of New York’s wealthiest and most infamous real-estate empires helped him acquire what...