The bigger issue is the vast disruption that would occur in the transition to more autarky.
America's economy is configured for designing iPhones, not assembling their components;
the innards of its cars and planes cross national borders many times before the final product is ready.
Faced with tariffs, firms have to redirect labour and capital to replace imports.
Some analysts attribute Mr Trump's presidency to the economic shock from trade with China after 2000.
The turmoil caused by reversing globalisation would be just as bad.
One estimate puts American job losses from a trade war at 550,000.
The hit to China would also be severe.
Any adjustment would be prolonged by Mr Trump's unpredictability.
Without knowing whether tariffs might rise or fall, what company would think it wise to invest in a new supply chain?
It is difficult to imagine such a realignment without a global recession.
Tariffs temporarily push up inflation, making it harder for central banks to cushion the blow.
The flight to safety accompanying any global downturn would keep the dollar strong, even as America's fiscal stimulus peters out after 2019.
So be wary.
The trade war may yet be contained, to the benefit of the world economy.
But America is the engine of global growth. In Mr Trump, a dangerous driver is at the wheel.