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Donald Trump thinks that slashing spending will reduce the federal deficit. Fair enough. It will. But would his proposed cuts reduce the deficit by $10 trillion over the next decade? CBO thinks he’s off by several trillion dollars. Here’s why:

Trump believes that his cuts would supercharge the economy and get it to 3 percent annual growth. CBO, which is required to be reality-based, figures his cuts would increase growth by about 0.1 percent. That puts long-term growth at 2 percent per year.

Of course, CBO isn’t taking into account the effect of Trump’s massive tax cuts for the rich. That’s because they don’t exist. Trump himself, however, is under no such constraints, and his budget simply assumes the tax cuts will happen and the results will be spectacular. When you can say anything you want, that’s the kind of fantasy you come up with.