A U.S. ban of TikTok began to take effect on Sunday, capping a high-stakes battle that pitted the federal government against one of the nation’s most popular social media platforms.

Congress passed the measure last spring with overwhelming bipartisan support, granting TikTok a 270-day window to cut its ties with China-based parent company ByteDance or face a ban.

Instead of initiating a sale, however, TikTok pursued a legal challenge on First Amendment grounds that ended in failure at the Supreme Court on Friday.

The unanimous ruling from the nation’s highest court found merit in national security concerns regarding potential user data collection or content manipulation that the Chinese government might undertake.

Yet the ultimate fate of TikTok remains uncertain. Rather than force TikTok to take the app dark, the ban targets third-party companies like cloud-service providers and app stores, meaning TikTok could circumvent such restrictions, at least temporarily.

The platform became unavailable for some users Saturday evening, with a popup message in the app saying, “Sorry, TikTok isn’t available right now.” By Sunday morning, App stores run by Apple, Google and Samsung began removing the app.

The Biden administration said earlier this week that it would not enforce the ban on Sunday, leaving implementation of the measure to President-elect Donald Trump, who takes office on Monday. Trump has vowed to reverse the ban.

Here’s what could be next for TikTok.

TikTok’s quality is expected to worsen

TikTok could remain available for U.S. users over the coming days and weeks but the app would likely degrade in quality, experts previously told ABC News.

The reason is because the ban would place restrictions on app stores and hosting companies, which provide the digital infrastructure on which web services like TikTok depend.

Mandatory withdrawal of the app from major app stores would not only bar new users from downloading the app, it also would prevent existing users from updating it.

Apple in a support update posted on Sunday said users who already installed ByteDance apps will be able to keep them on their device.

“But they can’t be redownloaded if deleted or restored if you move to a new device,” Apple said. “In-app purchases and new subscriptions are no longer possible.”

Without updates, the app would worsen in quality over time, some experts said – for example, through inconveniences such as video-loading delays and performance glitches.

A separate stipulation in the ban would also make it illegal for hosting companies to provide services for TikTok. The measure offers a fairly broad characterization of such firms.

TikTok would stop functioning if the firm’s U.S.-based hosting companies stopped providing services. However, the social media giant could establish partnerships with hosting companies outside the U.S., putting them out of reach of U.S. enforcement – in theory, at least.

Such a move would keep TikTok available to U.S. users, but the service would likely be slower and glitchier as the digital infrastructure moves farther away, experts said.

Trump has vowed to reverse the ban

Trump is considering what executive actions he has available to allow TikTok to keep operating, sources familiar with the matter told ABC News.

One option is an executive order that could attempt to direct the government to not enforce the law, but that avenue faces legal roadblocks, experts told ABC News, chief of which is that an executive order can’t override a law that Congress has passed and that has now been upheld by the Supreme Court.

Trump’s Justice Department could still opt against enforcement of the law, reassuring app stores and cloud-service providers that they wouldn’t face prosecution in the event of a violation.

While the Justice Department has enforcement discretion, app providers like Apple and Google could still be subject to hefty fines under a law that has a five-year statute of limitations, which would extend it beyond the length of Trump’s presidential term.

Pam Bondi, Trump’s nominee for attorney general, declined to say during her confirmation hearing this week whether she would commit to enforcing the TikTok ban.

TikTok CEO Shou Zi Chew, who will attend Trump’s inauguration after receiving an invitation from the incoming administration, thanked Trump in a video posted to TikTok on Friday after the Supreme Court ruling.

“I want to thank President Trump for his commitment to work with us to find a solution that keeps TikTok available in the United States. This is a strong stand for the First Amendment and against arbitrary censorship,” Chew said.

Congress may take up the ban a second time

TikTok may await a potential repeal of the law that banned the app in the first place.

A repeal would require passage in both houses of Congress, landing the measure on Trump’s desk for his signature.

Congress voted in favor of the ban only nine months ago. In the House of Representatives, the ban passed by an overwhelming margin of 352-65. In the Senate, 79 members voted in favor of the measure, while 18 opposed and three abstained.

Since then, however, Trump has voiced his disapproval of the measure and Republicans have taken control of both chambers of Congress. Even so, whether such a repeal would make its way to the floor, and its fate should it do so, are impossible to forecast.

ABC News’ Selina Wang, Katherine Faulders, Steven Portnoy, Elizabeth Schulze and Devin Dwyer contributed to this report.