The federal ban on TikTok took effect Sunday, but President-elect Donald Trump has indicated he will probably reinstate the app when he returns to office a day later—though he may have limited options to stave off a ban, and any attempts to stop it could be challenged in court. (Follow live updates on the TikTok ban here.)

“SAVE TIKTOK,” Trump posted on Truth Social early Sunday morning.

Americans who try to access the platform as of Sunday are greeted with a pop-up stating that they “can’t use TikTok for now,” but adding: “We are fortunate that President Trump has indicated that he will work with us on a solution to reinstate TikTok once he takes office.” TikTok CEO Shou Chew responded to the Supreme Court’s decision in a video Friday and committed to working with Trump on a solution to the ban. The CEO thanked Trump for his “commitment to work with us to find a solution that makes TikTok available in the United States,” adding TikTok is “grateful and pleased to have the support of a president who truly understands our platform.” “Rest assured we will do everything in our power to ensure our platform thrives ... for years to come,” Shou told U.S. users.

The Biden administration said Friday it will defer to Trump on enforcing the TikTok ban, given it takes effect on the last day of President Joe Biden’s term. “Given the sheer fact of timing, this Administration recognizes that actions to implement the law simply must fall to the next Administration, which takes office on Monday,” Press Secretary Karine Jean-Pierre said following the court’s ruling.

Trump will officially become president at noon on Monday, so he could theoretically intervene immediately after taking the oath of office. He told NBC News if he decides to grant TikTok a 90-day extension, he will “probably announce it on Monday.”

Trump told NBC he will likely extend the ban for 90 days, calling the move “appropriate,” but added: “We have to look at it carefully. It’s a very big situation.” Trump has been “mulling” a range of options on how to handle TikTok, the Post reported last week. In addition to an executive order that would pause the law from taking effect for a few months, Trump has reportedly considered issuing an order that would “unravel the law”—which is all but certain to result in legal challenges, given the policy was passed by Congress with bipartisan support and presidents cannot unilaterally repeal federal laws. The Times similarly reports Trump could use an executive order to declare the law won’t be enforced, or that it won’t be enforced only temporarily until a deal is reached. Trump is reportedly eager to “make a deal” with TikTok and ByteDance, per The Post, with allies floating options that could include forcing a sale of TikTok’s U.S. assets in a way that would give the U.S. Treasury a cut of the proceeds, or revive TikTok’s “Project Texas,” a plan TikTok previously offered to the Biden administration about how it could handle the U.S.’ national security concerns without separating from ByteDance. Experts cited by the Post suggested China—which would have to approve any sale by ByteDance—would only be likely to cut a deal with Trump on TikTok as part of broader political negotiations between the two governments.

While Trump could just declare his administration won’t enforce the TikTok ban, it’s hard to say whether that would actually work. Justice Brett Kavanaugh questioned Solicitor General Elizabeth Prelogar on Friday about that possibility, and Prelogar acknowledged Trump could order it not to be enforced and while it remains to be seen what the effects of that would be, there may be “safeguards” to legally protect companies who keep TikTok up as a result of his promises about facing penalties. Legal experts have suggested companies aren’t likely to take the risk and potentially subject themselves to legal liability by keeping up TikTok even if Trump says it’s fine, however, given the possibility that Trump could change his mind and decide to start enforcing the ban. “You could have a policy not to enforce this ban,” University of Washington Law School professor Ryan Calo told The Times. “But I think that maybe conservative companies would just be like: ‘OK, you’re not going to enforce it. But it is on the books, and you could enforce at any time.’”

Several investors have expressed interest in buying the platform, TikTok and ByteDance so far haven’t shown any interest in separating, with TikTok arguing in a court filing that doing so is “not possible technologically, commercially, or legally.” It remains to be seen if the company will change its mind should the Supreme Court uphold the law and it actually takes effect, however, and Prelogar suggested Friday that justices upholding the ban could be the “jolt” that ByteDance and TikTok need to actually start the divestment process. Trump could also potentially have an impact on forcing ByteDance’s hand, as James Lewis, director of the Strategic Technologies Program at the Center for Strategic and International Studies, told NPR that China could be persuaded to approve of ByteDance selling TikTok in exchange for Trump backing off his threat of high tariffs on Chinese imports. A source familiar with ByteDance’s thinking told The Post that reports TikTok could serve as “part of a big bargain or a big negotiation” were “legitimate.”

TikTok shut itself down for U.S. users shortly before midnight, right ahead of the ban’s Sunday start date, effectively preventing Americans from using its mobile app or website. The platform says users can still log in to download their data. TikTok said in a court filing that banning internet service providers from hosting the app means the company could no longer “provid[e] the services that enable the TikTok platform to function, effectively shutting down TikTok in the United States,” and TikTok’s lawyer Noel Francisco reiterated that Friday, saying it’s his understanding that if the ban takes effect, “we go dark.” Oracle also wouldn’t be allowed to host TikTok’s U.S. user data, as it does now. TikTok has told its U.S. employees they will still have jobs and the company’s U.S. offices will remain open even if the ban takes effect, The Times reports.

Yes, the ban is expected to similarly impact ByteDance-owned apps CapCut and Lemon8.

The Supreme Court upheld the TikTok ban in an unsigned opinion Friday—meaning it’s unclear if any justices voted against the law—ruling the ban does not violate TikTok and its users’ First Amendment rights, as the plaintiffs claimed. Justices ruled the federal government’s national security concerns about TikTok justified imposing the ban and singling out TikTok over other social media apps, and opposed TikTok and content creators’ arguments that the law silences their speech. The federal law “neither references the content of speech on TikTok nor reflects disagreement with the message such speech conveys,” justices argued, even as they acknowledged the policy “certainly burdens [TikTok’s] users’ expressive activity in a non-trivial way.”

If the ban does block TikTok’s U.S. user data from being hosted by a U.S. company, it’s possible the data that TikTok already has on its American users could be moved to China, which a Forbes investigation found is what happened when India similarly banned the app. That would actually make it more likely the data could be accessed by the Chinese government, contrary to the federal law’s national security goals.

President Joe Biden signed the bill requiring TikTok to leave ByteDance or else be banned into law in April, reflecting a bipartisan concern that the app poses a threat to national security. TikTok has long denied any wrongdoing or links to the Chinese government, but Forbes has reported numerous concerns involving the app, including TikTok spying on journalists, promoting Chinese propaganda that criticized U.S. politicians, mishandling user data and tracking “sensitive” words. The specific evidence the government has for justifying TikTok’s ban has not been made public, however, and was entirely redacted in court filings. TikTok and creators on the app sued to block the law days after it was enacted, arguing the ban unlawfully infringed on their First Amendment rights. A panel of federal judges sided with the government’s argument that the ban was justified due to the national security threat and did not violate TikTok’s First Amendment rights, given that users can still post on the app if it just separates itself from ByteDance. The court ruled the law as it was enacted is actually a less restrictive way of handling the government’s concerns about TikTok, given the fact it still allows the company to operate in the U.S. if ByteDance divests from it. TikTok appealed the case to the Supreme Court after the lower court declined to pause the law from taking effect, and the Supreme Court quickly took it up, scheduling arguments for Jan. 10 but declining to pause the law in the meantime.