in 1932 when the US was going into very heavy debt from bailing out all the states going broke from the Great Depression's 25% unemployment. Millions of people were losing their homes from not paying their prop taxes etc. The congress and Hoover wanted to start a national sales tax but there was a huge avalanche of hate mail for that idea. So the only option left was to tax the rich when they raised it from 20% to 63%, the largest peacetime tax increase in US history.
These days we just put it on the credit card and increase our national debt more and more giving the Republicons the excuse to cut social spending which was one of their prime strategies since the 1970s', called the "Two Santa Clause theory". google it if you want more info.
The top rate went from 15% to 70% in 1917 with WW1 and from 63%v gradually up to 94% during WW2.
So unfortunately, it may take another huge national crisis or depression to raise the top tax rate again more than a few percent.