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When the Supreme Court hears arguments on Friday over whether protecting national security requires TikTok to be sold or closed, the justices will be working in the shadow of three First Amendment precedents, all influenced by the climate of their times and by how much the justices trusted the government.

During the Cold War and in the Vietnam era, the court refused to credit the government’s assertions that national security required limiting what newspapers could publish and what Americans could read. More recently, though, the court deferred to Congress’s judgment that combating terrorism justified making some kinds of speech a crime.

The court will most likely act quickly, as TikTok faces a Jan. 19 deadline under a law enacted in April by bipartisan majorities. The law’s sponsors said the app’s parent company, ByteDance, is controlled by China and could use it to harvest Americans’ private data and to spread covert disinformation.

The court’s decision will determine the fate of a powerful and pervasive cultural phenomenon that uses a sophisticated algorithm to feed a personalized array of short videos to its 170 million users in the United States. For many of them, and particularly younger ones, TikTok has become a leading source of information and entertainment.

As in earlier cases pitting national security against free speech, the core question for the justices is whether the government’s judgments about the threat TikTok is said to pose are sufficient to overcome the nation’s commitment to free speech.

Senator Mitch McConnell, Republican of Kentucky, told the justices that he “is second to none in his appreciation and protection of the First Amendment’s right to free speech.” But he urged them to uphold the law.

“The right to free speech enshrined in the First Amendment does not apply to a corporate agent of the Chinese Communist Party,” Mr. McConnell wrote.

Jameel Jaffer, the executive director of the Knight First Amendment Institute at Columbia University, said that stance reflected a fundamental misunderstanding.

“It is not the government’s role to tell us which ideas are worth listening to,” he said. “It’s not the government’s role to cleanse the marketplace of ideas or information that the government disagrees with.”

The Supreme Court’s last major decision in a clash between national security and free speech was in 2010, in Holder v. Humanitarian Law Project. It concerned a law that made it a crime to provide even benign assistance in the form of speech to groups said to engage in terrorism.

One plaintiff, for instance, said he wanted to help the Kurdistan Workers’ Party find peaceful ways to protect the rights of Kurds in Turkey and to bring their claims to the attention of international bodies.

When the case was argued, Elena Kagan, then the U.S. solicitor general, said courts should defer to the government’s assessments of national security threats.

“The ability of Congress and of the executive branch to regulate the relationships between Americans and foreign governments or foreign organizations has long been acknowledged by this court,” she said. (She joined the court six months later.)

The court ruled for the government by a 6-to-3 vote, accepting its expertise even after ruling that the law was subject to strict scrutiny, the most demanding form of judicial review.

“The government, when seeking to prevent imminent harms in the context of international affairs and national security, is not required to conclusively link all the pieces in the puzzle before we grant weight to its empirical conclusions,” Chief Justice John G. Roberts Jr. wrote for the majority.

In its Supreme Court briefs defending the law banning TikTok, the Biden administration repeatedly cited the 2010 decision.

“Congress and the executive branch determined that ByteDance’s ownership and control of TikTok pose an unacceptable threat to national security because that relationship could permit a foreign adversary government to collect intelligence on and manipulate the content received by TikTok’s American users,” Elizabeth B. Prelogar, the U.S. solicitor general, wrote, “even if those harms had not yet materialized.”

Many federal laws, she added, limit foreign ownership of companies in sensitive fields, including broadcasting, banking, nuclear facilities, undersea cables, air carriers, dams and reservoirs.

While the court led by Chief Justice Roberts was willing to defer to the government, earlier courts were more skeptical. In 1965, during the Cold War, the court struck down a law requiring people who wanted to receive foreign mail that the government said was “communist political propaganda” to say so in writing.

That decision, Lamont v. Postmaster General, had several distinctive features. It was unanimous. It was the first time the court had ever held a federal law unconstitutional under the First Amendment’s free expression clauses.

It was the first Supreme Court opinion to feature the phrase “the marketplace of ideas.” And it was the first Supreme Court decision to recognize a constitutional right to receive information.

That last idea figures in the TikTok case. “When controversies have arisen,” a brief for users of the app said, “the court has protected Americans’ right to hear foreign-influenced ideas, allowing Congress at most to require labeling of the ideas’ origin.”

Indeed, a supporting brief from the Knight First Amendment Institute said, the law banning TikTok is far more aggressive than the one limiting access to communist propaganda. “While the law in Lamont burdened Americans’ access to specific speech from abroad,” the brief said, “the act prohibits it entirely.”

Zephyr Teachout, a law professor at Fordham, said that was the wrong analysis. “Imposing foreign ownership restrictions on communications platforms is several steps removed from free speech concerns,” she wrote in a brief supporting the government, “because the regulations are wholly concerned with the firms’ ownership, not the firms’ conduct, technology or content.”

Six years after the case on mailed propaganda, the Supreme Court again rejected the invocation of national security to justify limiting speech, ruling that the Nixon administration could not stop The New York Times and The Washington Post from publishing the Pentagon Papers, a secret history of the Vietnam War. The court did so in the face of government warnings that publishing would imperil intelligence agents and peace talks.

“The word ‘security’ is a broad, vague generality whose contours should not be invoked to abrogate the fundamental law embodied in the First Amendment,” Justice Hugo Black wrote in a concurring opinion.

The American Civil Liberties Union told the justices that the law banning TikTok “is even more sweeping” than the prior restraint sought by the government in the Pentagon Papers case.

“The government has not merely forbidden particular communications or speakers on TikTok based on their content; it has banned an entire platform,” the brief said. “It is as though, in Pentagon Papers, the lower court had shut down The New York Times entirely.”

Mr. Jaffer of the Knight Institute said the key precedents point in differing directions.

“People say, well, the court routinely defers to the government in national security cases, and there is obviously some truth to that,” he said. “But in the sphere of First Amendment rights, the record is a lot more complicated.”