Since returning to office, Donald Trump has embarked on a shock-and-awe policy blitz that has paralyzed not only his political rivals but also an automotive industry that had largely welcomed his return.

Carmakers may care little about Elon Musk’s government job cuts, or the United States taking Russia’s side against Ukraine. Efforts to eradicate D.E.I. policies are a little trickier, but auto executives and dealers have skillfully navigated such situations in the past. Still, this trade war — and rapid sequence of policy flip-flops — is not what they envisioned in a second Trump presidency.

“So far what we’re seeing is a lot of costs and a lot of chaos,” said Ford’s chief executive, Jim Farley. Paul Jacobson, General Motors finance chief, told investors that while a short tariff spat would be easily manageable, a “permanent” one would require billions of dollars in investment that might prove unneeded as soon as Mr. Trump’s term is over. “We can’t be whipsawing the business back and forth,” he said at a Barclays conference.

Making cars requires large investments, committing to products that last longer than presidential administrations, and factories that typically operate for decades, even generations. Before Mr. Trump’s election last year, auto folks were grousing about how hard it is to plan and invest when policies can change drastically every four years. Now they’re seeing the rules of the economy shift every four weeks — or four days.

To sum up the past six weeks: First, Mr. Trump announced plans for 25 percent tariffs on Canadian and Mexican imports — flushing away the trade agreement he negotiated in his first term. For decades, the auto industry has been investing billions in developing an efficient supply chain throughout North America. When Mr. Trump announced the levies on vehicles, engines and other components from Canada and Mexico, he jeopardized that entire project.

Then came the deadline dithering. First, the tariffs were set to take effect on Feb. 1, then Feb. 4, then March 4. With the stock markets tanking, Mr. Trump gave the auto industry another one-month delay for most automotive imports, which was expanded the next day to a vast array of other goods, from avocados to air-conditioners.