> Genuine questions: what can be done in a democratic setting to stop him?

Thiel is only "relevant" because he's wealthy.

In a system that allows wealth to equal political power, systematically weakening the impact of wealth on civic and political systems is an effective method. Whether that can be done in America, with the current understanding of the constitution and the current philosophy that many take towards taxation/wealth is questionable; but the idea that we can do nothing is just not true. We don't need to slide back into an era of 19th century robber barons and pseudo-aristocracy. If we do, it's because we largely gave up or allowed it to happen.

The difference to robber Baron this time is that those companies have gone global, so a new Teddy Roosevelt being elected in USA wouldn't help, because these multinationals can just extend outside jurisdiction. Which is very similar to the actual dynamic of states/federal that Teddy tackled [1]

Unfortunately the political rhetoric have smeared "the globalists" and equated people that want global coordination to limit those multinationals with power, with the ones abusing it. Even the platform that was promising to drain the swamp turns out was just another swamp, so one would need to start from the scratch for that political movement.

[1] https://youtu.be/ItKtQCAZHhg?is=-h_05pyB-37MHVJB