TikTok flickered back to life in the United States on Sunday after President-elect Donald J. Trump said that he would issue an executive order to stall a federal ban of the app.
The abrupt shift came just hours after major app stores removed the popular social media site and it stopped operating for U.S. users as a federal law took effect on Sunday. The company said in a post on X that in “agreement with our service providers, TikTok is in the process of restoring service.”
Mr. Trump said in a Sunday morning post on Truth Social that he would “issue an executive order on Monday to extend the period of time before the law’s prohibitions take effect, so that we can make a deal to protect our national security.”
The ban stems from a 2024 law that requires app stores and cloud computing providers to stop distributing or hosting TikTok unless it is sold by its Chinese parent company, ByteDance. Lawmakers passed the law over concerns that the Chinese government could use the app, which claims roughly 170 million United States users, to gather information about Americans or spread propaganda.
App stores and cloud computing providers that do not comply with the law face potentially significant financial penalties. Mr. Trump said in his post on Sunday that his order would “confirm that there will be no liability for any company that helped keep TikTok from going dark before my order.”
The possibility of an executive order, followed by TikTok’s stunning about-face, mark a new phase in the fight over the future of the app, which has reshaped the social media landscape, defined popular culture and created a living for millions of influencers and small businesses that rely on the platform.
In issuing an order, Mr. Trump would raise questions about the rule of law in the United States. His action would constitute an attempt to temporarily neuter a law that passed with broad bipartisan support in Congress and that the Supreme Court unanimously upheld last week.
“We thank President Trump for providing the necessary clarity and assurance to our service providers that they will face no penalties providing TikTok to over 170 million Americans and allowing over 7 million small businesses to thrive,” TikTok said in a statement announcing that the app was coming back online.
Creators celebrated as TikTok sputtered back to life.
“ITS BACKKKKK,” James Charles, a beauty influencer, posted on Instagram, where he had been communicating with fans since the ban took effect.
Policy experts and lawmakers from both sides of the aisle issued early warnings that the law is still valid and enforceable. TikTok remained unavailable for downloads on the Google and Apple app stores, suggesting that some companies continued to enforce the ban.
Legal experts said that the impact of Mr. Trump’s action would hinge on the details of any order he released, which is likely to provoke significant questions about the reach and limits of the president’s authority.
“There’s no good path here from a rule of law perspective,” said Alan Rozenshtein, an associate professor of law at the University of Minnesota.
Google declined to comment. Apple did not respond to a request for comment, although it said in an explanation on its website that it is “obligated to follow the laws in the jurisdictions where it operates,” and that TikTok would no longer be available for downloads or updates in the United States.
Oracle, which hosts TikTok on its servers, did not immediately respond to a request for comment.
It is unclear whether Mr. Trump’s efforts — and the negotiations to keep the app online that happened before he even takes office on Monday — will be successful in the long term. His executive order could face a legal challenge, including over whether he has the power to stop enforcement of a federal law. Companies subject to the law may determine that the text of an order does not provide enough assurance that they will not be punished for violations.
The law does allow a president to grant a 90-day extension if a buyer is found, but only if there is “significant progress” toward a deal that puts TikTok in the hands of a non-Chinese company. That deal also has to be able to be completed within the 90 days for the president to trigger the extension. And it’s unclear if that extension option still exists, given that the law is already in effect.
In his post on Sunday, Mr. Trump floated the idea that he “would like the United States to have a 50% ownership position in a joint venture,” without providing further details.
TikTok has said that a sale is impossible, citing the nature of its global operations, and China has already signaled that it could block the export of its all-important video-recommendation technology.
Some policy experts said there is too little information to draw a conclusion about the next steps. “What Trump has proposed on social media seems lawless,” said Peter Harrell, a former Biden administration official. “We’ll have to see what he actually does to implement it.”
Late Saturday, TikTok posted a message for users saying that the site was unavailable but, it was “fortunate that President Trump has indicated that he will work with us on a solution.”
Then, after restoring service, TikTok welcomed back users with a message saying, “As a result of President Trump’s efforts, TikTok is back in the U.S.!”
TikTok and several Democratic members of Congress in recent days mounted a last-ditch effort to keep the app online. Senator Chuck Schumer of New York, the Democratic leader, privately told President Biden that the app going dark on his watch would hurt his legacy.
Critics of TikTok started their own push to keep the possible ban on track. Senator Tom Cotton, Republican of Arkansas and chairman of the Senate’s intelligence committee, called some of the major tech companies in recent days to say they needed to comply with the law, according to three people familiar with the calls. He also said in a joint statement earlier Sunday that there was no room for any type of extension, since the law had already taken effect.
After TikTok announced it would restore service to the app, Mr. Cotton posted a warning.
Any “company that hosts, distributes, services, or otherwise facilitates communist-controlled TikTok could face hundreds of billions of dollars of ruinous liability under the law,” not just from the federal government but also state attorneys general, shareholder lawsuits and under securities law, he said in a post on X.
“Think about it,” he said.
Maggie Haberman, Karen Weise, Sapna Maheshwari, Madison Malone Kircher and Aaron Krolik contributed reporting.