When presidential historian Doris Kearns Goodwin began working five years ago on her newest book, Leadership in Turbulent Times , she didn’t know how apropos it would be to today’s political climate. The Pulitzer Prize-winning author profiled four presidents — Abraham Lincoln, Theodore Roosevelt, Franklin D. Roosevelt and Lyndon Johnson — who led the nation through some of its most difficult times. In the book, Kearns Goodwin chronicled their extraordinary strength and leadership acumen. She shared her insights on the Knowledge at Wharton radio show on SiriusXM . An edited transcript of the conversation follows. Knowledge at Wharton: Is there a bit of irony in the timing of the release of this book? Doris Kearns Goodwin: When I started it five years ago, I had no idea how relevant it would be to be studying these four leaders who lived in turbulent times.…