In a report published Tuesday, the World Trade Organization slashed its forecast for global trade growth for this and next year. And a closely watched gauge of American manufacturing showed factory activity slowed in September, the second straight month of decline.

Trade tensions between the United States and the European Union have already been running high. The governments announced in mid-2018 that they would work toward a trade agreement, but negotiations quickly stalled over a dispute about agriculture, which the United States insists should be included in the talks. Mr. Trump has been fiercely critical of Europe for selling more to the United States than it purchases and is considering hitting the eurozone with additional tariffs this fall on cars exported to America.

“They have not been treating this country right for many, many years, and they know it,” Mr. Trump said of Europe on Wednesday as he met with the president of Finland.

The Trump administration has also fiercely criticized the World Trade Organization itself, for overreaching its mandate and failing to restrain China’s poor economic practices. The United States is withholding appointments to a body of the organization that considers appeals to trade disputes, which will stop the organization from being able to complete new cases like the one against Airbus as of Dec. 10.

Stephen P. Vaughn, a partner at King & Spalding and the former general counsel of the trade representative’s office, called the Airbus ruling a “huge, huge win for the U.S.” but said it also demonstrated the limitations of an international system that the Trump administration has often criticized as slow and ineffective.

“It’s taken 15 years to get here, and it is highly unlikely that the Europeans will comply” with ending the subsidies, Mr. Vaughn said.

Chad P. Bown, a senior fellow at the Peterson Institute, said the planned exchange of tariffs highlighted the failure of the United States and Europe to work together to write more comprehensive rules about global trade, particularly subsidies. That could have major implications for China, which the United States and other countries have criticized for unfairly subsidizing its companies and undercutting other companies around the world.