For Bernard Arnault, France’s richest man and head of the LVMH Moët Hennessy Louis Vuitton luxury goods empire, the year started off brightly. His friend President Trump extended a personal invitation to the inauguration on Jan. 20. Consumers in the United States, one of LVMH’s biggest markets, were snapping up the company’s Dior dresses and Tiffany jewelry.

Then came Mr. Trump’s tariffs — and a substantial plunge in the company’s share price.

“Until the end of February, everything was going very well,” Mr. Arnault told a packed auditorium of anxious shareholders Thursday at the LVMH annual general meeting in the Louvre Museum in Paris. “Then we came up against a global economic geopolitical situation that was turned upside down by potential customs duties.”

Now, he said, it is up to European leaders to resolve the trade war with Mr. Trump “amicably.” Any failure would be “the fault of Brussels,” he added, and would force LVMH to increase U.S. production and “avoid Europe.”

Echoing a suggestion made recently by Elon Musk, one of Mr. Trump’s chief advisers, Mr. Arnault also called on European politicians to press for the creation of a free-trade zone between Europe and the United States.

LVMH is by no means the only global conglomerate to be whipped by Mr. Trump’s effort to rewire global trading. But as the world’s biggest luxury company, with 75 star brands, including Louis Vuitton, Christian Dior, Tiffany and Dom Pérignon Champagne, it has become an industry bellwether.