THE POWER BREAKER:

The historian had been hoping to visit Vietnam in March as part of his research for his Johnson book, but postponed the trip. He needs to looks through some papers in the Johnson presidential library in Austin, Texas, but is resigned to waiting indefinitely. "That's a great frustration," he acknowledged.

Meanwhile, he is so immersed in one section of the last Johnson volume, set during 1967, that he is not leaving for his more rural and presumably safer home on Long Island until he's done. The section, he says, "is as long as many books," a description his many readers would find easy to believe.

Caro began the Johnson books in the mid-1970s, around the time he turned 40. He has completed four volumes, totaling more than 3,000 pages, and has outlived many of his key sources. He was loathed by some Johnson loyalists for his second book in the series, "Means of Ascent," which presented Johnson as a boorish man and a singularly ruthless and unprincipled politician. But the mood shifted after Vol. III, "Master of the Senate," published in 2002 and a defining chronicle of Johnson's legislative genius that politicians today still study.

His most recent book, "The Passage of Power," came out eight years ago this month. Its story ended in mid-1964, with Johnson on the verge of passing an extraordinary run of legislation that had many celebrating him as a fulfiller -- and even exceeder -- of the hopes and vision of the assassinated John F. Kennedy.

But by 1967, when Joan Didion wrote "the center was not holding," the country and Johnson's presidency were unraveling. Riots devastated Detroit and Newark, New Jersey, among other cities; hundreds of thousands of troops were in Vietnam; inflation was taking hold and Congress was resisting continued funding for his Great Society domestic programs.

"He's in a moment of crisis," Caro says. "I'm trying to show in this section of this book what it's like to be president of the United States when everything is going wrong." [...]

"Bob has an unusually devoted following among readers because he has a powerful narrative voice that lends high drama to everything that he describes," fellow historian Ron Chernow wrote in an email to the AP. "Those who don't read biography imagine that great length is a deterrent. But genuine readers of biography crave stories on an epic scale and that Bob always delivers reliably and brilliantly."

In the new book, Caro plans a takeout on what it was like to be elderly before the passage, in 1965, of Medicare. Talking about his section on 1967, he explains that Johnson had once been confident that the country could fight wars both home and abroad -- defeat the North Vietnamese overseas and conquer poverty in the United States.

By 1967, "he's found out that he's wrong, although he doesn't admit that he's wrong," Caro said.

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