What is ever permanent? Not only can any tax provision be changed by Congress at any time, they can be made retroactive to prior tax years. I grant you that automatic expirations force legislative action, or some automatic change if no action is taken.

But that's besides the point about the accuracy of 10 year projections. They always rely on all kinds of assumptions (far beyond just a tax rate) that really can never be valid 10 years out.

I do have a very different viewpoint about corporate tax rates, which is simply about making the US a competitive tax jurisdiction in a steadily integrating world economy (despite Trump's efforts to exclude the US from it).