Higher prices. Disrupted supply chains. Wavering exports.

Those are some of the ways that some of Europe’s biggest companies have been affected by President Trump’s trade war, offering a preview of how tensions in global commerce could begin to ripple through the European economy.

As companies like BMW, Siemens and Volkswagen reported otherwise solid earnings this week, they warned that Mr. Trump’s aggressive stance on trade presented them with a host of new risks, which may already be acting as a drag on growth.

The president’s tariffs have not just raised the costs of materials like steel, they have also diverted trade worldwide and warped the complex global supply systems that businesses rely on. Here in Europe, there are signs of strain, which, along with risks ranging from Britain’s withdrawal from the European Union to the excessive debt loads of Italy and Greece, are piling pressure on the region’s economy.