As Commerce Secretary Wilbur Ross argued in a CNBC interview on Friday, for most consumer items we’re discussing trivial amounts of “tax” — an extra fraction of a penny for the can that contains Campbell’s Soup, a few tenths of a percent on the price of a new car.

Steel imports were worth about $30 billion in 2017, and aluminum imports around $17 billion, according to government data. Even in the simplest possible way of thinking of the potential cost of the new tariffs — just applying the 25 percent tax on steel and 10 percent tax on aluminum the president plans — we’re talking about only $9 billion. And that’s before accounting for the resulting shift toward domestic production that is the entire point of the policy.

More complex modeling would be needed to produce a reliable estimate of the cost of the tariffs, but the point is about the order of magnitude. These are not numbers that are enough to cause much damage to a $20 trillion economy, or to justify the $460 billion decline in the value of the stock market that took place between Thursday’s open and Friday midday.

This market drop makes more sense if you look at the president’s announcement not in terms of what it means for imported steel and aluminum, but rather what it says about the president himself.

The most consistent economic idea running through President Trump’s decades in public life has been a conviction that the United States is being duped in the global trade arena. He has denounced China, called for ripping apart the North American Free Trade Agreement, and accused generations of American trade negotiators of being incompetent.