First consider the average tax rates paid by the wealthy over a 65 year period:
As the tax rates have dropped, the share of national income going to the wealthy has increased, as shown below:
When the graphs are put together so the share of national income is compared to the tax rates, we can see there is a clear relationship between tax rates and the proportion of the total income that goes to the wealthy - when tax rates are higher, they get a smaller share of the national income and vice versa:
Of course, the national income is a zero-sum game, so it's also not surprising that the share of national income going to labor has the opposite trend - rising when tax rates are higher and decreasing when tax rates are lower:
The actual growth of our economy simply isn't related to the top tax rates - no matter how much the supply-siders wish it were. Low tax rates merely give the wealthy larger slices of the national pie - the idea that they'll bake more is really pie in the sky.
Lowering tax rates only increases the cow pie.