The trade war is the biggest threat to global growth.
On June 15th the White House confirmed that a 25% tariff on up to $50bn of Chinese imports would soon go into effect.
Three days later, after China promised to retaliate,
the president expanded, by as much as $400bn, the other goods America is threatening to tax.
If he follows through, nine-tenths of roughly $500bn-worth of goods imported from China each year will face American levies.
Meanwhile, the European Union is poised to impose retaliatory tariffs in response to America's action against EU steel and aluminium.
No wonder markets have caught the jitters.
The president is unafraid of escalating trade disputes because he believes he has a winning hand.
America buys from China almost four times as much as it sells there, limiting China's ability to match tariffs.
The White House hopes this imbalance will lead China to yield to its demands,
some of which (cutting the theft of American firms'intellectual property) are more reasonable than others (shrinking the bilateral trade deficit).
But Mr Trump overestimates his bargaining power.
If China runs out of American goods to tax, it could raise existing tariffs higher.
Or it could harass American firms operating in China.
More important, the president's mercantilism blinds him to the damage he could inflict on America.
He thinks it is better not to trade at all than to run a trade deficit.
This folly also dictates his tactics towards Canada, Mexico and the EU.
Mr Trump could yet withdraw from the North American Free-Trade Agreement and slap tariffs on cars.
The problem is not that America depends on trade.
In fact, it is a big enough free-trade area for the eventual damage to GDP, even from a fully fledged trade war,
to be limited to a few percentage points (smaller, specialised economies are more dependent on trade and would suffer a lot more).
Such self-in-flicted harm would impose a pointless cost on the average American household of perhaps thousands of dollars.
That would be bad, but it would hardly be fatal.