Make-or-break moments in a career often startle by how they appear at a moment's notice, no matter how much time is spent in preparation.

For David Frost, it came when former U.S. president Richard Nixon asked HIM a question. It was near the end of their 1977 interview about the Watergate scandal that drove Nixon from office three years earlier.

To mark the 35th anniversary of Nixon's resignation and capitalize on interest created by the "Frost/Nixon" movie, PBS is replaying that interview, starting Aug. 3 in the New York area.

The broadcast hasn't lost power with the passage of time. If anything, it's even more fascinating as a historical document, the experience richer after the movie filled in the back story.

Nixon hoped to salvage some dignity from a shattered career, and make money. He was paid $600,000 for a series of interview sessions on various topics, plus a portion of the broadcasts' profits. (Frost suggests that wasn't too much, given the expenses involved.)

Frost had cobbled together a makeshift network to televise his work. He was well-known in Britain as a TV host, but not in the U.S., and Mike Wallace's condescending attitude toward Frost during a "60 Minutes" interview typified the suspicion of many journalists that he wasn't up to the job.

The "Frost/Nixon" movie depicts Frost as playing down to those expectations during many of the interview sessions. He contends now that some cinematic exaggeration was at work but, still, he studied extra hard when Watergate was the topic.

The first part of the interview plays out like a boxing match. Frost has facts and jabs with them relentlessly, and Nixon learns he won't be scoring a quick knockout.

There are some fascinating asides: Nixon can't even speak the names of Washington Post investigative reporters Bob Woodward and Carl Bernstein, he finds them so distasteful. He predicts, erroneously, that no future president would be impeached because he wouldn't want to put the country through the tumult of a Senate trial.

As the interview wound down, Frost knew he didn't have enough. Nixon had acknowledged mistakes; history demanded more.

Frost asked Nixon if he thought the word "mistakes" was enough.

"What word would you express?" Nixon replied, flashing one of those smiles that he'd use at inappropriate times.

It was heart-stopping, Frost recalls.

He took a breath, then came up with a detailed, three-part response. Americans wanted to hear him say that Watergate was more than a series of mistakes, it was wrongdoing, whether criminal or not. They wanted to hear him acknowledge that he abused the power of his office. And they wanted to hear him say that he put the country through two years of needless agony, and that "unless you say it, you're going to be haunted for the rest of your life."

"That was totally off-the-cuff," Frost says now. "That was totally ad-lib. In fact, I threw my clipboard down just to indicate that it was not prepared in any way ... I just knew at that moment that Richard Nixon was more vulnerable than he'd ever be in his life. And I knew I had to get it right."

Even then, Nixon filibustered. Frost had to prod him again.

"I didn't expect this question, frankly," the former president said.

"Nor did I," Frost replied softly, his face drooping with exhaustion.

You can almost see, then, the calculation in Nixon's eyes. He looked beaten, too. And it seemed he decided right there to stop running.

He offered memorable remarks of regret, concluding that, "I let the American people down and I have to carry that burden with me for the rest of my life."

Everyone on the set realized what the moment meant, Frost said. Nixon had never addressed the subject quite so directly in a public forum, and wouldn't again.

"If you had gone to Richard Nixon six months (later) and asked if he regretted giving the interviews, he would have probably said yes, he did regret it, because he admitted so much more than he planned to admit, right down to the mea culpa at the end," Frost said.

"However, I think if you went back to him three or four years later he would have probably realized by then that he had to face up to these issues in a forum he did not control before the American people," he said. "There would have been a much greater cloud over him if he had never faced up to these issues."