For three decades, proponents of Supply Side Economics told skeptics "just watch and see what will happen!" (Whenever top tax rates were cut.) Okay, we've watched. And absolutely every large-scale forecast made by promoters of Supply Side Economics failed -- diametrically -- without major exception.
The uber-rich did not take their tax-break largesse and invest it in innovative/productive equipment. They poured it into either passive investments -- what Adam Smith derided as "rent-seeking" -- or else risky financial instruments and asset bubbles. Above all, the direct forecast that reduced revenues would erase federal deficits went directly opposite to observed fact.