Trump, the supposedly brilliant businessman, can't do basic math

Look, I can't help it if the Trump administration keeps lobbing these fat pitches.

Donald Trump's budget has a $2 Trillion Math Error:

One of the ways Donald Trump’s budget claims to balance the budget over a decade, without cutting defense or retirement spending, is to assume a $2 trillion increase in revenue through economic growth. This is the magic of the still-to-be-designed Trump tax cuts. But wait — if you recall, the magic of the Trump tax cuts is also supposed to pay for the Trump tax cuts. So the $2 trillion is a double-counting error.

It's astonishing.  Not only can Trump himself not do basic math (no big surprise there, actually) but no one in his administration can either.   Think about that.  Not a single person in the Trump administration caught this massive but ultimately trivial error.  This is second-grade math, folks.  There is no excuse for this.