Lost in the discussion of the effect of tax rates is the question of perspective. The Mellon tax cuts from above 70% down to 25% resulted in dramatic increases in tax revenues, as did the Kennedy cuts from 91% to 70% and the Reagan cuts from 70% to 28%. Revenue increases were almost immediate. However, W's cuts from 39.6% to 35% were not of the same magnitude, and it could be argued that revenue increases resulted instead from monetary policy. With minor rate changes, the effects on revenue are also minor.
What is important is the effect of rate changes on long term growth in the tax base. Above the 10% necessary to support core government functions, the effect on growth of a tax increase is always negative compounded into the future.