Free speech and national security can often conflict. During the Civil War, Abraham Lincoln prevented newspapers from publishing pro-Confederate material. During later wars, the federal government suppressed criticism. After the 9/11 attacks, Congress made it a crime to provide even human rights advice to extremist groups.

In each case, government officials argued that they needed to restrict speech to protect Americans. And in each case, free speech advocates argued that the government had gone too far and undermined the country’s values.

The same is true about the latest conflict between speech and security — involving TikTok, the social media platform owned by a Chinese company.

In response to concerns that China can use the platform to spy on Americans and spread propaganda, Congress last year passed a law requiring TikTok’s parent company to sell it to a non-Chinese owner. TikTok and the parent company, ByteDance, then sued to block the law. This morning, the Supreme Court will hear arguments in the case.

In today’s newsletter, I’ll lay out each side’s best arguments. Whatever your own views, I encourage you to recognize that there is no perfect solution, just as there was no perfect solution to the earlier conflicts between national security and free speech. Prioritizing one probably means compromising the other.

TikTok as speech

The argument to leave TikTok alone starts with its popularity. About 170 million Americans, equal to half the country’s population, use the app. They entertain themselves, communicate with friends, follow the news, go shopping and operate businesses.

Critics of the law say that shutting down TikTok — as the government would do if ByteDance refused to sell it — would be an unprecedented infringement on Americans’ speech: Never before has the government eliminated a platform used so widely for communication and commerce.

Critics also argue that Congress has failed to show that China uses TikTok to manipulate Americans; the law is instead based on the worry that China might one day do so. The law’s effect is “to substitute definite manipulation by our own government for feared manipulation by China,” Jameel Jaffer and Genevieve Lakier, two First Amendment experts, wrote in a Times Opinion essay.

Donald Trump now seems to be on TikTok’s side, too. In a brief last month, he and his lawyers argued that the Supreme Court should let him resolve the issue after becoming president. (The deadline for ByteDance to sell TikTok is Jan. 19.) Trump originally supported a forced sale but changed his position last year, evidently after speaking with a Republican Party donor who’s a TikTok investor.

TikTok as a threat

The argument in favor of the law revolves around the Chinese government’s recent actions and future ambitions. China treats companies as extensions of the state. If executives disobey orders, they can be fired or sent to prison. China has also made extensive efforts to spy on the U.S. and influence American politics.

Already, videos on some subjects, including Taiwan and Tibet, can be hard to find on TikTok, independent research has found. The same is true of pro-Ukraine and pro-Israel videos. (China has become increasingly allied with Russia and Iran.) These patterns suggest that TikTok suppresses material that the Chinese Communist Party doesn’t like.

Perhaps the simplest argument for the law is that the U.S. would not have allowed the Soviet Union to own NBC, Life magazine or a company that collected Americans’ personal information. “Limits on foreign ownership have been a part of federal communications policy for more than a century,” the legal scholar Zephyr Teachout wrote in The Atlantic.

Supporters say that this history helps explain why Congress passed the law overwhelmingly, with bipartisan support, and why both liberal and conservative appeals court judges voted to uphold the law last month.

Today’s oral arguments will offer a clearer sense of how the justices might rule. My colleague Adam Liptak, who’s a lawyer by training and covers the Supreme Court, says that recent history suggests TikTok may have the harder case to make. “The court will be reluctant to second-guess congressional judgments about national security even in the context of the First Amendment challenge,” Adam said.

He pointed to a 2010 case that involved another clash between national security and free speech. In that ruling, the court upheld a provision in the 2001 Patriot Act that banned even nonviolent assistance to terrorist groups.

Three of today’s justices (John Roberts, Samuel Alito and Clarence Thomas) were in the majority, and only one (Sonia Sotomayor) dissented. A fourth member of the current court (Elena Kagan) was the solicitor general in 2010 and defended the law during oral arguments.

But Adam added that the court could also draw on older precedents, from the Cold War and Vietnam eras, in which the court rejected the government’s arguments that supposed threats to national security justified limits on speech.

Politics

Opinions

Immigration policy needs three shifts: deterrence of illegal migration, an expansion of legal migration and a path to citizenship for those who already live here, the Editorial Board writes.

Big cities can be great places to live. New York should prove its greatness by reducing crime on the subway, Mara Gay writes.

Here are columns by David Brooks on character building and Michelle Goldberg on Representative Ro Khanna.

Espionage: A Chinese American scholar pretended to be a democracy activist and an ally to dissidents in New York. He turned out to be a spy.

Shop smarter: Can you spot ultraprocessed food? Take our grocery quiz.

Lives Lived: Anita Bryant was a singer and former beauty queen who had a robust career in the 1960s and ’70s. But her opposition to gay rights — she called homosexuality “an abomination” — virtually destroyed her career. She died at 84.

SPORTS

College football: Notre Dame beat Penn State in a 27-24 thriller to earn a slot in the national title game.

M.L.S.: The league apologized for publishing an article that identified the wrong player as having transferred to one of its clubs, Atlanta United.

ARTS AND IDEAS

Auction houses like Sotheby’s and Christies have been struggling in a market downturn. So they have expanded beyond art and are selling niche experiences and luxury goods, including real estate, classic cars, dinosaur fossils, designer handbags, jewelry, fine wines and game-worn N.B.A. jerseys. Read about the shift here.