BROOKE GLADSTONE: This week, the Senate Armed Services Committee debated whether to boost U.S. troop levels in Afghanistan. The historically daunting challenges posed by that place have led many pundits to invoke the quagmire of Vietnam, and this week President Obama was asked about it.

MALE CORRESPONDENT: Do you reflect on what happened to Lyndon Johnson and worry the same might happen to you?

PRESIDENT OBAMA: Well, I think that you have to learn lessons from history. On the other hand, each historical moment is different. You never step into the same river twice. And so, Afghanistan is not Vietnam, but the dangers of overreach and not having clear goals and not having strong support from the American people, those are all issues that I think about all the time.

DAN ELLSBERG: If he doesn't understand that we are in Vietnam now, or, as I think of it, Vietnamistan, he’s absolutely removed from reality.

BROOKE GLADSTONE: One could argue that you may be seeing the world through Vietnam-colored lenses.

DAN ELLSBERG: Absolutely. I agree, couldn't agree more.

BROOKE GLADSTONE: That’s Daniel Ellsberg, legendary leaker of the Pentagon Papers, a top secret history of failed policy and lies about America’s involvement in Vietnam. A new film about the man and his leak, called The Most Dangerous Man in America, opened this week in New York and will soon across the country. The film starts with the moment almost 40 years ago when he removed the documents from his safe at the Rand Corporation, left behind his clearances, his colleagues, his career as a Pentagon insider and risked prison to put the papers before the public. It culminated in a stunning 1971 Supreme Court decision in favor of press freedom. Ellsberg’s main regret is that he waited years to do what he did, a mistake he hopes isn't repeated.

DAN ELLSBERG: I'm sure there are many people in the Pentagon and CIA and the White House who are in my shoes right now. My advice to them is, don't do what I did. Don't reveal it six years from now. Don't wait ‘til the escalation has occurred. Instead, they should do what I wish I had done in 1965, and that is tell the public what I believed right then, that my president was making a terrible mistake and that Congress should hold hearings, Congress should demand the truth and Congress should set him straight. Just in the last two weeks, we have now learned that many Democrats are standing up and questioning their Democratic president. Where are they to get their information from, purely from the Cabinet ministers who are doing the - the President’s bidding?

BROOKE GLADSTONE: What is this material that you think ought to be leaked to the public?

DAN ELLSBERG: When you say “out there” should we say “in there”? What’s in the safes? What’s inside the Pentagon? What’s in the White House? I am sure there are estimates in the State Department Intelligence, INR, which was right about Iraq, right about Vietnam; I'll bet they're right about now. And what Congress should be hearing from them, if they were leaked, is that putting more troops in will strengthen our enemy, that putting those troops in, supporting them with drones, killing civilians, however many activists we may kill also, replaces those activists overnight, multiplies them as it did in Vietnam. Vice President Biden and General James Jones, the National Security Assistant, have doubts. That’s interesting. That gives us an opening here. But what are their doubts? What are the pieces of paper that have convinced them that have come over their desk? What are the estimates they're getting? Congress needs those, and the press needs those, the public needs those.

BROOKE GLADSTONE: So you don't anticipate that this government will supply the Congress with the kind of accurate information it would need to openly debate this issue.

DAN ELLSBERG: They've had eight months to do it and they haven't done it yet, and I don't expect them to do it.

BROOKE GLADSTONE: You’re sure this information is there? Do you have any proof?

DAN ELLSBERG: Am I sitting here with the documents from the administration? Certainly not. I haven't had access to those for a long time, except when they out years later, as in Iraq. I've got lots of documents now in books by Richard Clarke, in books by many others, of the information that was withheld from us by them, and others, for years. So I can look at the situation and, frankly, it’s my degree of identity with the people in those jobs. I acted in that for a dozen years. I've followed it very closely since. I follow the leaks that are going on.

BROOKE GLADSTONE: So what is the role of the leaker in this environment?

DAN ELLSBERG: There are a lot of people looking at estimates that are being withheld from the public, at plans for the next 50,000, the next 87,000 troops that are going in that the public is not going to be told about until after they're there. And I think they should ask themselves, did my oath to uphold and support the Constitution really permit me to keep quiet when I see the public being lied to? Now, I would hope that some of them, when they consider that, will consider taking a very great personal risk, even to their families, when it comes to income, to their status in society, possibly a risk of prosecution, and telling Congress information that they believe Congress ought to have in making these decisions, and the public ought to have, and they might save hundreds of thousands of lives.

BROOKE GLADSTONE: So what happens if this material that you believe exists inside of government gets out, is leaked, goes before the Congress, and nothing happens?

DAN ELLSBERG: That’s the question. What do we do about it? What do you do about it, what do I do I about it, and what does Congress do about it? The lesson that I’d learned, I think, from the Pentagon Papers, which set me to be an activist – it changed my life – was telling the truth has no guarantee that it will make for better policy, but it’s a better gamble than leaving it up to the president to make these decisions on his or her own.

BROOKE GLADSTONE: Dan, thank you very much.

DAN ELLSBERG: Thanks for having me.

BROOKE GLADSTONE: Daniel Ellsberg. The new documentary about him is called The Most Dangerous Man in America, partly because he managed to defeat the most powerful one, Richard Nixon.

RICHARD NIXON: I wanted to tell you that I was so damn mad when that Supreme Court had to come down. I didn't – first, I didn't like their decision, but -

J. EDGAR HOOVER: I didn't either.

RICHARD NIXON: Unbelievable, wasn’t it?

J. EDGAR HOOVER: It was unbelievable!

RICHARD NIXON: You know, those clowns we’ve got on there, I - I’ll tell you, I hope I outlive the bastards.

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BROOKE GLADSTONE: Up next, whether you’re an exhibitionist or excruciatingly shy, the Internet can make you worse. This is On the Media from NPR.