In Author in Chief (Avid Reader, Feb.), historian Fehrman examines the tradition of U.S. presidents as authors.

What inspired you to look at presidents through the lens of their authorship?

It was 2008 and I was in grad school, but what I was really doing was going to Politico’s website and clicking refresh way too much. I was obsessed with the presidential campaign, and I was struck by Obama’s books and the enormous reaction to them. I wanted to see—is there a history here? How did this start? What other books have made this kind of impact?

What was the biggest surprise?

The biggest big picture surprise was just how important these books had been. They’ve changed careers, they’ve won campaigns, they’ve been enormous bestsellers. In terms of individual presidents, Lincoln was the big surprise. I knew he loved books, and I knew he didn’t have many growing up, but I didn’t know that he wrote a book. I was surprised how hard he worked to assemble it. He knew before many people did how a book could help make somebody president.

Which presidential book was your favorite?

Calvin Coolidge’s autobiography. He had a great sense of humor, and he was a really fine and simple and spare writer—the kind of writing that looks easy but isn’t. He didn’t try to defend his policies or get into legislative squabbles. He just tried to say, “This is what it feels like to be president as a human being.” And that included the passing of his son while he was in the White House.

I wasn’t expecting Coolidge to play such a large role in the book. It was really illuminating to see why people voted for him.

He’s not what you would expect a politician to be. He’s not a big talker; he’s not in love with himself. So why was he such an effective politician? I think it’s because he was good at using his odd qualities to make himself seem authentic, but he was also just a really good writer. He wrote really good speeches, too.

How did you select which presidents and books you were going to include?

I tried to find the most interesting stories. I wanted people to love the details and to be excited to talk about the book. Some of the moments I’m most proud of are when John Quincy Adams sits down and reads Thomas Jefferson’s autobiography, or when Ronald Reagan reads Calvin Coolidge’s autobiography. I love the idea of presidents as readers, and I tried to tell the overarching story of how their books influenced other people and the genres themselves. I spent 10 years on this; I had a lot more I could have put into it. It’s pretty short by presidential book standards.