If I understand Jonathan Chait correctly, the Trump administration is acknowledging that their budget would result in two trillion fewer dollars being collected in revenues over the next decade. But they are insisting that two awesome things will happen. The first is that this actually won’t happen because greater economic growth will produce the revenue after all. And the second is that this greater economic growth will also allow them to balance the budget.
For Chait, this is a simple error of arithmetic. It’s an example of double counting. First they assume two trillion in extra revenue based on higher economic growth (to make up for lower tax rates/fees), and then they assume an extra two trillion a second time (to bring the budget into balance)....