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.)

TikTok went dark for American users in an unprecedented display of the U.S.-China divide over technology and national security.The app started halting service Saturday night for 170 million users in its most important market shortly before a law took effect requiring it to shed its Chinese ownership or close in the U.

President-elect Donald Trump says he wants service providers like Apple and Google to put TikTok back online in the US, and proposed creating a joint venture where the US owns 50 percent of the app.