"..................Jarrett’s official job description is “somewhat vague,” Becker writes, noting that at least part of her role is to serve as “chief liaison to the business community, state and local governments, and the professional left,” but her influence is undeniable. She commands a staff of nearly three dozen and has a hand in decisions ranging from the invitation list to state dinners and what gifts to give foreign leaders, to who should be nominated to the Supreme Court, appointed to a vacant ambassadorship, or awarded the President Medal of Freedom. When Warren Buffett visits to the White House for lunch,...