I had limits on how much I could use legally. What were the limits on how much you could quote from King’s speeches and writings? The lawyer for the family told me that they would not be participating. I tried very hard to get interviews with King’s children.

I don’t think she’s gotten enough credit. Of all the people who passed away before I started, I especially miss (speaking to) Coretta Scott King. Historians have done a good job preserving those voices in oral histories and audiotapes. What are the challenges of writing such a biography when so many of King’s colleagues have died? It tells you he’s not prepared for this, and he was vulnerable to that kind of anxiety all of his life. The fact that he has what we would describe today as a panic attack tells you a lot. He realized it was going to change his life. In your retelling of King’s speech in Montgomery, Alabama, just before the bus boycott began, he seems as if he doesn’t know what he’s walking into. It’s a tragic chapter in American history that didn’t have to happen that way. To me what we see is one of the greatest relationships ever between a Democratic president and an activist is undermined by racism and paranoia, by obsession over a man’s sex life for no good reason, other than their obsessions. And if King is alive, who knows what would have happened? Some of what he’s trying to tell us about income inequality and fair wages and reparations sinks in and becomes law. Well, King might still be alive for one thing. If Johnson had told Hoover to back off, what would have happened? The important news is how unbelievably aggressive the F.B.I. We already knew King was not faithful to Coretta. (Stegall was Johnson’s closest personal aide and his primary liaison with the F.B.I.) Writing several times a week, she shows that Johnson was far more complicit than we knew, encouraging the campaign to surveil and harass King. I was able to get LBJ’s library to release, for the first time, hundreds of pages of documents, maybe in the low thousands, from Mildred Stegall’s files. What new declassified documents did you use? There’s not been a straightforward hefty King bio since 1982, which was Stephen Oates’ book “Let The Trumpet Sound.” That’s way too long. How many Lincoln biographies are there? There are new ones every two years.

The darkest king