- President Donald Trump has made attacking the press a hallmark of his presidency, railing against what he considers fake news and calling journalists the enemy of the people.

- These public attacks may be unprecedented, but when it comes to the press, he shares at least one thing in common with his predecessors, the struggle to keep government secrets from leaking.

The modern battle against leaks can be traced back to a high stakes attempt to stop them by President Richard Nixon more than four decades ago.

- [Richard] Right, well, Monday at noon, officially?

Well, let's wait 'til then.

Fine, (breathes sharply) okay.

Nothing else of interest in the world today?

- [Al] Yes sir, very significant.

This goddamn New York Times expose of the most highly classified documents of the war.

- [Richard] Oh that, I see.

I didn't read the story, but you mean that, that was leaked out of the Pentagon?

- [Celeste] On June 13th, 1971, The New York Times began publishing a trove of secret documents called the Pentagon Papers exposing how president after president had misled the American people about their country's role in escalating the Vietnam War.

- [Richard] What in the world do responsible publishers think about, to put out trunkloads of secret documents?

- [Felix] And it's getting worse every day.

- [Richard] It's awful, isn't it?

- The lawyers that represented The Times had already given dire warning that publication could subject them to prosecution under the Espionage Act, that they could lose their television licenses, that the publisher could go to jail.

All said with a very high-level of intensity.

- [Celeste] But The Times refused to stop publication, saying the American people had the right to know the hidden calculations behind the war.

Nixon turned to the courts to stop them.

(dramatic instrumental music) - [Richard] Right to know, that's, of course, a goddamn code word.

Right to know.

The public has no right to know secret documents.

What The Times has done is placed itself above the law.

- It was very unusual for the government to go to court to try to stop publication of anything, but the idea of the government going to court with respect to an on-going news story was all but unknown.

- [Celeste] For Nixon, the case was about more than stopping a leak.

He wanted to undercut the press.

- [Richard] Let's make something out of it.

It's an opportunity.

- This issue-- - [Richard] Listen, The New York Times, believe me, The New York Times can be discredited for...

Indefinitely as a result of this.

In fact, I'm going to.

- There's more at stake in this debate than one newspaper series or even one major breach of security, sooner or later we can expect this issue to come before the Supreme Court and the question there will be the role of the press in a democracy.

- [Celeste] The answer came quickly, in a six to three ruling that affirmed the Times' right to publish the classified reports.

Citing the need for checks on government power, the Justices said that the Nixon administration had failed to prove that the release would cause any imminent harm.

- It was very embarrassing for President Nixon to have gone to court and lost and have the Supreme Court write an opinion vindicating the press that he hated so much.

- [Celeste] But Nixon wasn't finished.

- [Richard] I just say that we've got to keep our eye on the main ball, the main ball's Ellsberg.

We gotta get this son of a bitch.

(dramatic instrumental music) - [Celeste] Using a World War I statute meant to punish spies, Nixon's justice department indicted Daniel Ellsberg, the military analyst responsible for leaking the Pentagon Papers to The Times.

- I was tried for a violation of what is commonly described as the Espionage Act because it's usually used for espionage, but I was tried under it for a non-espionage offense.

- [Celeste] Unlike a spy, Ellsberg's intention was not to help a foreign government.

He wanted to reveal the truth about the Vietnam War to the American people.

- [Fred] Daniel Ellsberg says he leaked the Pentagon Papers because the government lied and concealed facts about the Vietnam War.

- We won't the killing, but this trial will inform the American public, in ways that it's never heard before, of how we've governed in the past quarter century and what censorship and deception do to a democracy.

- I'm not for espionage, I don't know anyone who is, and I'm not against criminalizing that.

The question is, should it be criminal to inform your fellow citizens of things that, on the face, they aught to know.

- [Celeste] That question was left unanswered as the Watergate Scandal enveloped the Nixon administration.

- The president said that in 1971, he formed an investigative unit inside the White House to fight what he called national security leaks.

One of the first things the people in that unit did was to burglarize the offices of Daniel Ellsberg's psychiatrist.

- With Watergate breaking out, and with the revelation of the crimes they'd taken against me, by an almost miraculous set of events, my charges were dismissed.

- No, not you.

Not you, you're organization's terrible.

Your organization's terrible.

Let's go, go ahead.

- [Jim] Sir, sir-- - Quiet, quiet.

- The press would like-- - Go ahead.

She's asking a question, don't be rude.

- [Jim] Can you give us a-- - Don't be rude.

- [Jim] Give us a question-- - Don't be rude.

No, I'm not gonna give you a, I'm not gonna give you question.

You are fake news.

(intense instrumental music) - [Celeste] Almost five decades after the Pentagon Papers, the Trump administration is waging its own battle.

- I think the media's the opposition party.

- [Celeste] With the press.

- The press has become so dishonest that if we don't talk about it, we are doing a tremendous disservice to the American people.

- [Celeste] While his public attacks might be unprecedented, another part of his strategy is not, going after those who leak to reporters.

- We're gonna find the leakers.

They're gonna pay a big price for leaking.

- [Celeste] But Trump didn't have to look all the way back to Nixon for a roadmap, his predecessor provided it.

- If we can root out folks who have leaked, they will suffer consequences.

- [Celeste] Over a span of four years, the Obama administration charged eight people with violating the Espionage Act for sharing government secrets with the press, more than all previous administrations combined.

Matthew Miller was a senior official in the Obama justice department.

- If you look the way, then you only encourage other people to leak national security secrets.

You do have to show that there are consequences for leaking information that could harm national security and the only way to do that is to prosecute some of the individuals responsible for the most egregious leaks.

(dramatic instrumental music) There are secrets that need to remain secret.

- [Celeste] Miller says that keeping secrets secret became more challenging in the digital age.

Massive leaks of classified information by Edward Snowden and WikiLeaks showed how vulnerable secrets had become.

- We begin tonight with that mountain of secret wartime information exposed in the press today, more documents than the Pentagon Papers during Vietnam.

- [Celeste] But in trying to control leaks, Obama moved into territory that other presidents had largely avoided.

- I'm sitting at my desk and I get an email that looks like it's from the Department of Justice.

I'm not sure what it is and I look at Matt and I said, "Matt, what is this, is this spam?"

And I said, "It's not spam.

"The government just took our phone records.

- [Celeste] In May of 2013, former Associated Press reporters Matt Apuzzo and Adam Goldman learned that the government had seized their phone records during an investigation into who leaked details of a CIA operation in Yemen.

The dragnet scooped up records from phones used by more than 100 reporters and editors.

- One thing we heard again and again from prosecutors was, "Well, of course we took the phone records "for your editors and your colleagues "and your bureaus and swept everybody up, "'cause that's exactly how we would investigate a gang."

Well, we're not a gang, we're a newsroom and the right to deal drugs isn't in the Constitution, so there should be a recognition that what happens in the news gathering process is a little different.

It felt like it was just an investigation intended to send the message, don't talk to reporters.

- Yeah.

- It had the desired effect.

- [Celeste] In the case of a classified leak at Fox News, the Obama justice department went so far as to imply that correspondent James Rosen, because of his reporting, could be charged with a crime.

- [Reporter] In court papers, an FBI agent said Rosen, "asked solicited and encouraged" a source to give him sensitive information about North Korea and that he was a possible "co-conspirator" for violations of the Espionage Act.

- Not 'til that moment had the United States government ever characterized the behavior of a journalist as being that of a co-conspirator to a crime for asking questions about government policy.

- That the Obama-Holder justice department-- - [Celeste] Rosen was never charged, and following a media outcry, the Obama administration reigned in some of the more aggressive tactics used to obtain journalists' records.

- We must enforce consequences for those who break the law, but a free press is also essential for our democracy, that's who we are.

And I'm troubled by the possibility that leak investigations may chill the investigative journalism that holds government accountable.

- While there's a necessity to protect national security, there is also an enormous need for an informed public.

And so, while one can justify certain prosecutions of leakers, the risk of them is that it does provide a roadmap for a hostile administration to really try to bring the press down.

- [Celeste] Since taking office, the Trump administration has increased the number of leak investigations and aggressively prosecuted leakers.

At least five people have been indicted under the Espionage Act, including Julian Assange.

- The US leveling more than a dozen new charges against WikiLeaks founder Julian Assange.

- [Celeste] But this is only one way the current president has worked to change the public narrative of his administration.

- Fake, fake, disgusting news.

(crowd cheers) - [Crowd] CNN sucks, CNN sucks, CNN sucks!

- And just remember, what you're seeing and what you're reading is not what's happening and I'll tell you-- - I think, in this day and age, the value of the unofficial story, the story that has not been sanctioned by the government, that value is greater than it's ever been.

- [Celeste] Having lived through the Nixon administration, Daniel Ellsberg says it's critical that no president is given the power to dictate the truth.

- Can you really have democracy in a real sense with the government having the final voice and the total voice as to what citizens shall know about what they're doing and whether they're telling the truth and whether they're obeying the law?

I would say no.

If they have the last word and the citizens can only know what the government tells them, it's a mockery of a democracy.

(dramatic instrumental music)