The Most Dangerous Man in America: Daniel Ellsberg and the Pentagon Papers tells multiple stories, of which two are central: The former Rand Corporation analyst's shift from hawk to dove, and the process of releasing those famous Defense Department documents to congressmen, and later, to major newspapers. It's the latter tale that provides the tension in this unexpectedly gripping account of the Pentagon Papers case. And no mistake, if The Most Dangerous Man isn't as edgy as a fictional thriller, it's much more suspenseful than the typical after-the-fact documentary.

Narrated by Ellsberg himself, the movie follows its protagonist's disillusionment as it blossoms into the decision to copy the 7,000-page secret report on the war's conduct. (His teenage kids helped.) Then the focus switches to The New York Times, The Washington Post and the Boston Globe — and the lawyer who won a landmark Supreme Court ruling against prior restraint of news reports.

The movie's off-screen chorus consists of Richard Nixon and his aides, including Henry Kissinger (the man who dubbed Ellsberg so "dangerous") and Alexander Haig. Their coarse and angry comments, taken from the White House tapes that helped end Nixon's political career, evoke both the spirit of the times and the ex-president's character: Using the sort of boilerplate outrage common to him, Nixon accuses Ellsberg of providing "aid and comfort to the enemy."

It's a dubious charge. The Pentagon Papers contained a history of the Vietnam War that revealed how presidents all the way back to Truman had deceived the American people; they didn't include current military information that might have helped the Viet Cong and the North Vietnamese.

Ellsberg was not one of the new-left zealots who wished for Ho Chi Minh's victory. As The Most Dangerous Man shows, he was a former Marine Corps second lieutenant who considered that position the most satisfying job he ever had. What turned Ellsberg against the war was not sympathy for the Vietnamese — although he deplored indiscriminate bombing of civilians.

In part, it was personal experience: Leading a patrol in 1966, he received a firsthand lesson in the difficulties of guerrilla war against an entrenched enemy. Ellsberg was also dismayed by the gap between the public certainties and private doubts of men like his one-time boss, Defense Secretary Robert McNamara. So Ellsberg began to leak documents to members of Congress. When that didn't work, he went over their heads to the readers of The New York Times.

Ehrlich and Goldsmith found plenty of interesting archival images, especially for the lesser-known first half of the story. But they sometimes rely on Errol Morris-style reconstructions of events, which are less deft than Morris'. Distractingly, they also use sketchy animation for a few sequences.

Mostly, though, The Most Dangerous Man in America lives up to its subject's importance. It's not only a fine introduction for viewers who don't remember the Vietnam era, but also offers some revelations to those who thought they knew it reasonably well. Copyright 2010 National Public Radio. To see more, visit http://www.npr.org/.