It's not clear that the president's action is legal, but there are laws such as those empowering CFIUS to review acquisitions of US companies by foreign buyers

It's not clear that the president's action is legal, but there are laws such as those empowering CFIUS to review acquisitions of US companies by foreign buyers (in this case, musical.ly) for any national security implications. These national security implications are probably far-fetched, but there's some theoretical basis for action here...