The highest one I see is a 94% tax on income over $200,000 in 1945. First of all, that was towards the end of a World War during which we developed an entirely new kind of bomb. Nothing our government is currently doing requires that level of commitment from its citizens. Second, that income bracket in 1945 would be at $2.676 million today [1]. Even the top 0.1% of US incomes today start at just $1.6 million [2]; a tax bracket like the 1945 one would have barely any people in it.

[1]: https://www.wolframalpha.com/input/?i=US%24200000+%281945+US...

[2]: https://en.wikipedia.org/wiki/Affluence_in_the_United_States...