>"Added together, the total net worth for 2018's billionaires was US$9.1 trillion" https://en.wikipedia.org/wiki/The_World%27s_Billionaires
Meanwhile, the US federal government spends ~$4 trillion per year: https://en.wikipedia.org/wiki/United_States_federal_budget#/...
So even confiscating all the wealth of the top couple thousand richest people in the world (not just US) would only fund the US government for 2-3 years. And that would be a one-time event.
Basically, the amount of money spent by the US government is already so massive that I don't see how giving it more can possibly help with anything. It would be much more realistic to attempt making the government slightly more efficient and then reallocating the money saved.
And that ignores that barely anyone will end up paying these 90% taxes, just like almost no revenue was collected from the 90% bracket in the 1950s since various accounting methods/etc were be used to avoid it.