Six months into his new administration, Mr. Trump’s assault on global trade has lost any semblance of organization or structure.

He has changed deadlines suddenly. He has blown up negotiations at the 11th hour, often raising unexpected issues. He has tied his tariffs to complaints that have nothing to do with trade, like Brazil’s treatment of its former president, Jair Bolsonaro, or the flow of fentanyl from Canada.

Talks with the United States were like “going through a labyrinth” and arriving “back to Square 1,” said Airlangga Hartarto, the Indonesian minister for economic affairs, who met with U.S. officials in Washington on Wednesday.

The resulting uncertainty is preventing companies and countries from making plans as the rules of global commerce give way to a state of chaos.

“We’re still far away from making real deals,” said Carsten Brzeski, global head of macroeconomics at the bank ING in Germany. He called the uncertainty “poison” for the global economy.

Gone is the idea that the White House would strike 90 deals in 90 days after a period of rapid-fire negotiation, as Mr. Trump pledged in April. Instead, Washington has signed bare-bone agreements with big trading partners including China, while sending many other countries blunt and mostly standardized letters announcing hefty tariffs to start on Aug. 1.