Keep in mind that it isn't necessary to fully ban it. Impairing a global Internet social media firm's reach is in the horseshoes and hand grenades domain where a moderately close to the target and imperfect ban is good enough to get the job done.
TikTok is a for profit enterprise. If U.S. operations become less profitable, then it won't have a reason to continue U.S. operations.
"TikTok primarily makes money through advertising, thus making it an attention-based business model."
(Source)
In particular, from the same source, it is the sixth highest generator of digital advertising revenues in the world.
A lot of that digital advertising revenue is from firms seeking to win over U.S. customers (mostly, U.S. firms or firms that do business in the U.S., often publicly held firms, and some of whom are governmental entities). The U.S. sourced advertising revenues of TikTok are about $6 billion a year in 2023. This is a majority of its $10 billion a year global advertising revenues.
Moreover, most of that business is brokered through intermediary digital advertising agencies which are easy regulatory targets. There are 45,000 digital advertising agencies in the U.S. and it isn't a particularly concentrated industry, but you could still have a huge impact just by targeting the top 100 of them or so - which is vastly easier than targeting the many tens of millions of U.S. users of TikTok.
A U.S. firm that advertises on TikTok, or a digital advertising agency with U.S. business that brokers advertising on TikTok, if TikTok is banned, is an easy enforcement target and mostly, publicly held companies and governmental entities comply with the law voluntarily as a matter of their broad, overall business policies/standard operating procedures.
Simply requiring each digital advertising agency to have its CEO certify under penalty of perjury that it doesn't do business with TikTok once a quarter on a one page form with no auditing except whistleblower driven enforcement would be more than enough to get mass compliance from the industry before really digging into serious enforcement investigations and prosecutions.
Throw in similar certificates of compliance from publicly held companies in their regularly quarterly reports and from governmental agencies, and you'd be well on your way to an effective ban.
Without revenues from firms and governments vulnerable to U.S. sanctions sending their advertising dollars to TikTok, U.S. operations just don't make sense for the platform and it will die (or dwindle to irrelevance) in the U.S. market.
Even if people who go out of their way can still access TikTok, if it isn't a source of revenue for the company, and if is less of a source of exposure for users who use it to get the word out about themselves, the ban would still work.
It doesn't necessarily take all that much of a nudge. TikTok is basically a fad that needs continued momentum to survive. If interrupted long enough, people will find alternatives and those users will be hard to win back.
For example, Windows Internet Explorer went from market dominance to irrelevance (despite being only slightly different from its competitors) with a far milder nudge from regulators - simply easing tying arrangements between operating system software and browsers due to anti-trust enforcement.
