Julian Assange ended his seven-year stay last month at the Ecuadorean Embassy in London, where he had sought refuge from prosecution in Sweden and the United States. The British Government has since ordered that he be extradited to the US, where he may be charged under the US Espionage Act.

In his role as founder and chief disseminator of WikiLeaks, Assange came under scrutiny in 2010 for publishing 250,000 classified American documents related to the Iraq and Afghanistan wars, including information on an arguably indiscriminate airstrike by the American military that became known as the “Collateral Murder video”.

WikiLeaks’ notoriety continued to grow after it leaked private documents from Hillary Clinton’s 2016 presidential campaign with the aid of the Russians. Observers were quick to draw comparisons between Assange’s work and the 1971 decision by The New York Times and The Washington Post to publish The Pentagon Papers, which detailed the US Government’s top-secret actions in Vietnam. In response, the Nixon Administration filed for prior restraint, the ability to censor such material before publication.

HuffPost noted strong parallels between Assange and Daniel Ellsberg, who leaked The Pentagon Papers, proclaiming that “another courageous ‘national security leaker’ has stepped forward and now is facing retaliation similar to what the US Government tried to inflict on Ellsberg”.

Alan Dershowitz concurred: “I believed then, and still believe now, that there is no constitutional difference between WikiLeaks and The New York Times.”

Is such a parallel apt? Not exactly. People misremember the Supreme Court decision in The Pentagon Papers cases that gave The New York Times the right to publish the documents. The court did not find a sacrosanct freedom of the press.

It merely allowed for the continued publication. Indeed, the justices’ split decision pointed in the other direction: that in matters of “mortal danger”, journalists have a legal responsibility not to publish.

The Pentagon Papers were a top-secret account of the Vietnam War commissioned in late 1967 by Secretary of Defence Robert McNamara. The review drew on classified documents from the Defence Department, the Central Intelligence Agency and the Joint Chiefs of Staff.

Although he was an architect of the war in Vietnam, McNamara had grown gravely concerned about the direction of the conflict. He ordered the exhaustive review to figure out how “a small nation of 17 million people ... could hold out against and defeat ... the greatest military power in the world”.

On June 13, 1971, three years after the completion of the study, The New York Times printed excerpts of the material. The paper received its copy from Ellsberg, a 40-year-old defence analyst who had worked on the project and who immediately became a champion to the antiwar Left for his willingness to risk jail to expose Government misdeeds in Vietnam. The leak infuriated Richard Nixon and much of his administration.

National security adviser Henry Kissinger deemed their predicament a “revolutionary” situation fomented by the hippies and longhairs opposing the war. Kissinger warned the president of “a wholesale subversion of this government”.

Thought to be under attack, Nixon bunkered down. Within three days, he ordered his attorney-general to halt the printing of the papers on the grounds that Ellsberg and The New York Times were violating the 1917 Espionage Act.

When The New York Times stopped printing The Pentagon Papers, The Washington Post took over publishing until it was also sued by the Government.

The cases of New York Times Co v United States and United States v Washington Post were reportedly the first in American history in which the Government sued newspapers for prior restraint.

Never before had prior restraint been declared on national security grounds. Within a span of days, The Wall Street Journal deemed the cases “probably the most sensational clash between press freedom and government censorship in American history”. The Supreme Court heard oral arguments at an exceptionally rare Saturday session. In the end, the court was so divided that, in an unusual move, the justices issued ten opinions.

Instead of the usual majority-subscribed “opinion of the court”, the justices offered an unsigned ruling, which Chief Justice Warren Burger read to a packed crowd of onlookers.

In three short paragraphs, the majority laid out a narrow verdict: the Government had neither demonstrated nor met the threshold to justify halting the printing. The court lifted the temporary stays against publication, and the Times and the Post were free to continue reproducing the papers.

Yet the short dictum offered neither a defiant championing of the free press nor a definitive bolstering of executive reach. Nine conflicting opinions and a bland unsigned holding left ample room for interpretation. The most pressing question was the standard of “mortal danger”.

Who most irresponsibly risked soldiers’ lives in wars such as Vietnam: an indiscrete press or a militant government?

The court’s liberal justices took the side of press freedom. Justice Hugo Black argued that the free press did not threaten soldiers’ lives. On the contrary, journalists had the right, even the mandate, “to prevent ... the Government from ... sending [young men] off to distant lands to die of foreign fevers and foreign shells”.

By contrast, the three most conservative justices were unequivocally on the side of security threats. The media’s loose lips threatened the lives of the nation’s youth. It was not for the Times to determine “the death of soldiers, the destruction of alliances, the ... difficulty of negotiations”.

Justice Harry Blackmun, who moved to the Left during his time on the court, pointedly wrote: “The First Amendment, after all, is only one part of an entire Constitution.”

The court’s two moderates split the decision, marring the clarity of the case. They joined with the majority to support the publication of the papers, but they joined the three conservative dissenters in upholding the Espionage Act.

Justice Byron White argued that the Government had not reached the “heavy burden” threshold. If it had, he wrote, newspapers would not be “immune from criminal action”.

In sum, most of the justices refrained from ruling that the freedom of the press was unlimited. Publishers might be held liable for what they printed, although only after publishing, not before — with prior restraint.

That is, Nixon might not be able to halt the publishing, but he might sue for damages after the fact. Because of the deep fractures in the court, the holding obscured how a non-binding majority of five found that in publishing sensitive material and secret documents, journalists and newspaper owners would neither be free of the Espionage Act nor clear of prison time.

The ambivalent ruling was misunderstood from the start. The media, by and large, reacted as if their victory was complete.

“The Pentagon Papers: Free At Last”, read a Washington Post headline. With the stay lifted and the papers able to resume publishing, the ambiguity of the ruling was lost. “It’s beautiful,” gushed the Post’s executive editor, Benjamin Bradlee. “It’s by far the most important thing I’ve ever been in involved in.”

The Wall Street Journal declared it a “stinging defeat for the Nixon Administration” as 15 newspapers, and then 345, reprinted materials from the Pentagon study.

A few presses did remain measured. The Boston Globe cautioned that newspapers could publish, but would continue to “publish at their peril”.

The San Francisco Chronicle ominously judged the decision a “silent warning”.

The Boston Globe had it right. The press may still “publish at their peril”. Assange has been charged on 17 counts of the Espionage Act for leaking hundreds of thousands of State Department documents disclosed by intelligence analyst Chelsea Manning. Discussion has focused on whether Assange is a journalist as a way of determining whether he is protected by the freedom of the press.

And yet, as the Pentagon Papers cases demonstrate, even if WikiLeaks is classified as a press outlet, precedent holds that there may be limits to the freedom of the press. Assange may still be prosecuted for publishing materials of what the Times then termed “mortal danger”.

The Supreme Court’s “silent warning” looms.

• Zachary J. Jacobson is a Cold War historian. He received his PhD from Northwestern University