LOL. Okay, he is not stating that the Rates should be 20%, but rather, no matter what the rates, the result is that the collections are 20% of GDP due to the operation of the economy as an inverse function of the rates...the higher the rates the slower the economy and the lower the collections, but it still can’t get above 20%. Lower the rates and the thing takes off and they still get 20% of a much larger pie. See, it’s what you really want.
Laffer Curve.