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I liked Binyamin Appelbaum’s historical comparison of the Trump tax cut with Reagan and Bush, although such a comparison risks suggesting that the previous rounds made sense. They didn’t. The Reagan tax cut caused a sharp reversal in the long-run trend toward a declining debt-GDP ratio, the Bush tax cuts undid the fiscal progress of the Clinton years. And conversely, the Clinton tax hike helped produce surpluses even as the economy experienced a large boom, totally the opposite of what the usual suspects on the right predicted.

That said, Trumpcuts are an even worse idea than Reaganomics, and not just because we start from much higher debt, the legacy of the financial crisis, which cut deeply into revenue and temporarily boosted spending. It also matters that we start from a much lower top tax rate than Reagan did.

Here’s the modern history of the top marginal rate:

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So Reagan was cutting taxes with a starting rate of 70%; Trumpcuts would start from only a bit more than half that. Why does this matter?

Actually, two reasons. First, tax cuts are supposed to spur growth by increasing the amount of an increment in income someone can keep for himself or herself. When you start from 70% taxation, cutting the rate 1 percent raises the take-home component by 1/30, or more than 3%. When you start from 39.6%, the same size cut raises the take-home slice by 1/60, or half as much. In other words, we’d expect the incentive effects of a given tax cut now to be only half what they were under Reagan.

And suppose for the sake of argument that you do get some extra growth. How much of this feeds back into higher revenue? That depends on the marginal tax rate — which is much lower now, only a bit more than half, than it was in 1981.

So even if you believed that voodoo economics worked under Reagan — which it didn’t — it would take a lot more voodoo, in fact around 4 times as much, for it to work now.

Which makes you wonder: how can they possibly sell this as a responsible plan? Oh, right: they’ll just lie.