How could it ever have been about national security?

Statesmen love to conflate national security with state security, because to a believing statesman, they're the same thing. And bonus, it opens the door to all kinds of rational i actions for abuses. Back when Trump wanted to ban tiktok, it was on the face because of the potential propaganda influence the Chinese had over the american youth via their algorithm, and of course partially framed as protecting our your from the moral panic that is social media. What it was really about was leverage, it's a pretty profitable business in China, and to balance influence, states nowadays have influence on one another's populations to varying degrees, and they seek to trade and ration that as well. The Democrats were against it because, who knows, they've got to be against everything Trump, or they think championing the opiate of the youth will win your votes, or they're CCP agents, pick your preferred explanation. In the 4 years since Trump left and re entered office, tiktok has shown itself to be a major force for the rightward shift of the youth. You can blame the algorithm, say that the Chinese wanted trump to win, who knows why it worked out that way, but it did, and so the Democrats decided to keep the rhetoric Trump built up about it for their own ends. And in that time, Trump has decided that it is very valuable to him politically to have so much support there, but still wants to control it, hence this "America owns half" thing. It's all disingenuous politicking. It's not just organized crime that is the state wanting it's cut, its people and organizationz within that over arching organization looking out for their political interests as well.