The US has previously had top marginal income tax rates even higher than 70%. As far as I can tell, currently the highest tax bracket is 37% at income over $600

The US has previously had top marginal income tax rates even higher than 70%. As far as I can tell, currently the highest tax bracket is 37% at income over $600,000. Why not add more brackets with progressively higher rates? The largest barrier is that usually to get elected to to the federal positions that are required to pass this policy you need the support of the donor class, exactly the constituency that would be opposed to the policy.