Sometimes in life, he said, there’s reason not to look back, but as he talked through Watergate and its consequences in Mr. Woodward’s living room in Washington, he said, he felt increasingly confident that “it’s the right time to take a look at this moment in history to inform the present.”

Mr. Woodward, in a separate interview, said that the men discussed: “What’s the legacy of Watergate? What do we understand? What are some of the lessons? It’s been a long time.”

The answers not only change over time, but they also remain up for debate. One of Nixon’s wars, Mr. Woodward said, “is a war against history” — intentionally speaking in the present tense. He cited a book review in The Wall Street Journal two months ago by Frank Gannon, a former Nixon aide, who asserted that many questions about the scandal remain unresolved. “How did a politician as tough and canny as Richard Nixon allow himself to be brought down by a ‘third-rate burglary’?” Mr. Gannon wrote. “Your guess is as good as mine.”