I can with 99.99% certainty say that the US tax code has played virtually no role in the rising disparity between the top 1% and the bottom 50%'s income wages. If anything it has helped "even the playing field" ever since the Bush tax cuts. Any policy prescriptions that look to reform the tax code to try to remedy this dynamic, will bare no fruits whatsoever. Education, training, entrepreneurism and innovation are the best options we have. Liberals believe that in order to remedy the rising disparity of incomes is to apply punitive taxation to the wealthy, and distribute those funds to their intended recipients. The logical way to approach this issue is to figure out a way to put the bottom 50% into a position to where they will earn more, rather than look to support them through welfare, subsidization and entitlement programs.
For one, added taxation does demonstrably slow economies down. Two, welfare and entitlements increase dependency and decrease production from many of these recipients. And three, subsidies by in large increase the price (inflation) of the underlying product.
It's time to begin looking for real solutions to this issue, rather than the same old liberal one's, which is to punitively tax more those that have and distribute it to those that don't, to simply even out the playing field.