The protective tariff is the tax that eats itself. These excises are intended to generate revenue for the federal government and to protect domestic industries from foreign competition, but the more they do of one, the less they do of the other. If there is much revenue being generated, then demand for imports remains high and domestic competitors are not being effectively protected; if the tariff is high enough to discourage imports, then it produces less revenue (here, economist Arthur Laffer smiles) because there isn’t any tax collected on the sales that don’t happen.

What tariffs mainly accomplish, then, is to distort markets, disrupt supply chains and increase costs for businesses and consumers. And because the Trump administration changes its tariff targets from day-to-day — or even from hour-to-hour — it introduces more uncertainty into the marketplace, which is a problem for any business but an enormous problem for a business with a product-development cycle measured in decades.