He continued: “I want to go to the great battlefields of Hue. I want to describe — there are a number of good books on this, but I always want to go for myself — what it’s like to fight in the jungle, because that’s really something we hadn’t really encountered.” He added, “There’s a lot of stuff I want to do.”

In addressing the subject of Mr. Caro’s age, Mr. Lamb brought up William Manchester’s three-volume life of Winston Churchill, which was completed by Paul Reid after Mr. Manchester’s death.

“I don’t want anybody to write a book with my name on it but me,” Mr. Caro said. “I don’t happen to think that was a very good idea, what happened with Manchester’s book. I’ve written an awful lot on power and as I say, I’m not rushing this last book. I’m trying to do it the same way as my other books. And I don’t want people to think that something is written by me when it’s not.”

Caro said he is now finishing a section of the book in which, in an “incredible burst,” in 1965, Johnson oversaw passage of the Voting Rights Act, Medicare, Medicaid and more than a dozen separate education bills. Mr. Caro called it a formative moment of just a few months, during which Johnson “rams through so much of what’s made America what it is today.”

Mr. Lamb also asked about the eventual home for his voluminous archives, which Mr. Caro called “a very important question that I happen to be wrestling with right now.” The author estimated that less than 5 percent of the material in his research files has made it into the finished books. “The most important thing for me,” Mr. Caro said of the files, “is to have them in a place where they’ll be accessible and properly indexed so researchers in the future can have them.” He added, “So that’s a real problem that I haven’t solved.”