Autos are hardly the only part of the manufacturing sector facing challenges. Factory employment, which fell from 17 million jobs two decades ago to about 11.5 million in 2010, has regained only 1.3 million jobs during the post-2008 economic recovery. Just 434,000 of those jobs were added after Mr. Trump took office.

Yes, automation played some role in lowering employment, but the bigger problem has been competition from countries like China that are now able to produce goods as well as we do or better using much cheaper labor. For carmakers, that has meant moving production to Mexico.

In addition to lost American jobs, the consequence of this competition has been lagging earnings for factory workers. Once paid a premium, manufacturing workers now earn below-averag e wages.

The president’s main policy response has been to start a trade war. Mr. Trump is correct that some countries — notably, China — don’t play fair, but his strategy has led only to acrimony, a jittery stock market and rising international tensions.

Even manufacturers don’t like the trade war. General Motors said that Mr. Trump’s tariffs on steel and other products would add $1 billion to its production costs, which puts more pressure on the company to cut workers.

Mr. Trump’s responses to G.M.’s decision also miss the mark. He called on G.M. to close one of its plants in China, even though G.M. doesn’t import a meaningful number of cars from there. He said G.M. should no longer have access to incentives to stimulate electric car production, which would simply damage the government’s effort to make the industry more competitive by spurring investment in new technologies.

Instead of Mr. Trump’s ham-handed approach to manufacturing, we should be pursuing more sophisticated remedies. I’m all for pushing back on the protectionist policies of China and other nations, but let’s do it with our allies and with the support of international organizations.