He settled on a Cobb salad and a bottle of Coke Zero.

John Wesley Dean III grew up in Ohio and attended high school at the Staunton Military Academy in Staunton, Va. There, he befriended Barry Goldwater Jr., a son of the five-term Republican senator from Arizona who would suffer a landslide loss to Lyndon B. Johnson in his 1964 presidential bid. Mr. Dean and Barry Jr. would visit the senator in Washington, and Mr. Dean was captivated.

“He was a very striking man,” Mr. Dean said. “He would take us around to the Senate. And you’d see all the people, the guards, make a wake for these two young guys following behind him.” He was also impressed by the senator’s car. “He had a Thunderbird when they were first out. It was rigged like the cockpit of an airplane. He had all kinds of meters and gadgets that didn’t come with the car. He had a two-way radio. He had a ham radio. He could talk to airplanes.”

Mr. Dean attended law school at Georgetown University and in July 1970, at age 32, was recruited to become White House counsel to the president. It didn’t take long for him to witness the underside of power. He told the story, after his Cobb salad arrived, of Scanlan’s, an upstart magazine that printed an article linking Vice President Spiro T. Agnew to a scheme to repeal the Bill of Rights and cancel the 1972 election. Just days after Mr. Agnew had condemned the story as fraudulent, Mr. Dean received an order instructing him to have Scanlan’s audited by the Internal Revenue Service. The assignment came from Mr. Nixon himself, Mr. Dean said.

“I thought, O.K., I don’t know much about Agnew, but I do know that this is so off the wall, and unlikely, that this is almost a joke,” Mr. Dean said. “I really wasn’t sure how to handle it.”

He sought the advice of a Nixon political adviser, Murray Chotiner. “He said, ‘John, this is a place that operates on need-to-know, and I don’t need to know this,’” Mr. Dean recalled. Mr. Chotiner made this argument, according to Mr. Dean: “Well, why can’t the president, who is the head of the executive branch, start an audit of any taxpayer he decides he wants audited?” Mr. Dean was dumbfounded, believing such an audit would be illegal. Mr. Chotiner persisted, Mr. Dean said. “He said: ‘I don’t want to get in a debate with you, but let me just give you some advice. If you don’t do it, he will find somebody who will do it.’”