Max Frankel, a New York Times reporter and editor who helped push for the publication of the Pentagon Papers, died Sunday at the age of 94.

A Pulitzer Prize-winning journalist, Frankel was well known for his decades of reporting. But it’s another piece of writing, not initially published in a newspaper, that holds a special place in First Amendment history.

An affidavit by Frankel filed in New York Times Co. v. United States, better known as the Pentagon Papers case, has become one of the most important public documents laying out the realities of national security reporting and Washington’s unspoken rules around government secrecy and leaks.

Initially drafted as a memo to the Times’ lawyers, Frankel’s arguments schooled lawyers, the courts, and anyone who believed government secrets should always be off limits to the press.

“What Frankel wrote became one of the most important documents in history of press freedom,” said James Goodale, who was the general counsel for the Times during the Pentagon Papers case. “Not only did it sway our outside lawyers to defend the case in court, but we turned it into sworn statement which helped sway the district court judge to rule in our favor.”

Frankel wrote: “Without the use of ‘secrets’ … there could be no adequate diplomatic, military and political reporting of the kind our people take for granted, either abroad or in Washington and there could be no mature system of communication between the Government and the people.”

Importantly, Frankel explained how government officials routinely reveal “secrets” to the press for their own purposes:

“Presidents make ‘secret’ decisions only to reveal them for the purposes of frightening an adversary nation, wooing a friendly electorate, protecting their reputations. The military services conduct ‘secret’ research in weaponry only to reveal it for the purpose of enhancing their budgets, appearing superior or inferior to a foreign army, gaining the vote of a congressman or the favor of a contractor. The Navy uses secret information to run down the weaponry of the Air Force. The Army passes on secret information to prove its superiority to the Marine Corps. High officials of the Government reveal secrets in the search for support of their policies, or to help sabotage the plans and policies of rival departments. Middle-rank officials of government reveal secrets so as to attract the attention of their superiors or to lobby against the orders of those superiors.”

Of course, what Frankel was defending was not the publication of secrets leaked purposefully by government officials, but rather the publication of a classified study of the Vietnam War leaked without authorization by whistleblower Daniel Ellsberg. But Frankel and other reporters knew that if they relied only on the official leaks, the public would only be getting part of the story — the part that benefited the government.

They also knew that classification wasn’t all it was cracked up to be. As Frankel explained in his affidavit, classification decisions aren’t always based on the national interest. He wrote that:

“the Government and its officials regularly and routinely misuse and abuse the ‘classification’ of information, either by imposing secrecy where none is justified or by retaining it long after the justification has become invalid, for simple reasons of political or bureaucratic convenience. To hide mistakes of judgment, to protect reputations of individuals, to cover up the loss and waste of funds, almost everything in government is kept secret for a time.”

The manipulation of classification decisions and strategic leaks to the press remain commonplace in Washington today, more than fifty years after Frankel laid it all out. Officials from both parties routinely make public secret information when it serves their purposes, from former CIA director David Petraeus, who leaked classified information to his biographer and received just a slap on the wrist, to President Donald Trump himself.

But what may be changing is the courage of news outlets and other institutions to stand up to government officials, as The New York Times, The Washington Post, and numerous other newspapers did when they published the Pentagon Papers and exposed the government’s lies about the Vietnam War.

It’s not easy to challenge government authority today, especially when the President and his cronies have made no secret of their desire to throw publishers, reporters, and sources in jail. But it also wasn’t easy for journalists and news outlets to challenge President Richard Nixon, who, until Trump, was perhaps the most anti-press president in our history.

Still, Frankel and others who worked on the publication of the Pentagon Papers chose to stick out their necks and stick up for press freedom. The result was the Supreme Court’s decision repudiating government prior restraints on the press in almost all circumstances, perhaps the most important press freedom decision today.

Unfortunately, there’s no guarantee that the Supreme Court today will be as willing to defend the First Amendment and the free press. But that makes it all the more important that reporters defend press freedom to the public and explain why it matters loudly and repeatedly.

Defending press freedom must mean defending the right to publish government secrets, even when the government objects. It also means defending the brave whistleblowers who make sure that the government doesn’t get to control what the public knows.

Enough time has passed that we’re losing some of the journalists and whistleblowers who fought for press freedom during the Nixon era. Today, we must look to their examples, and their words, to make the case that it’s necessary and right for the press to publish government secrets that inform the public.