You make it sound as though he put a lot of his own money (somehow obtained from elsewhere) into these companies.
But that's not true at all. It is correct English to say that he is "heavily invested" in these companies in the sense that his wealth is paper wealth based on the perceived value (stock price) of these companies.
But he is not invested in them the way that a typical person has their retirement funds invested in a company or mutual fund.
It’s got to be worth a try rather than the disastrous economic policies that got us here.
In the same vein, if the US were to implement a wealth tax, the simplest way in terms of enforcement and not creating perverse incentives to shelter wealth outside the country would be to make it international in scope. Yes, people could give up their citizenship, but that's a huge sacrifice which most wealthy people would not want to make at any price, and there's already an exit tax in place for people that do this.