By around 11:50 am, the CAC40 was down 1.6% to around 8,130 points, a drop broadly in line with the pan-European Euro Stoxx 50 index (-1.7%), while Wall Street remains closed today in observance of "Martin Luther King Day".

On Saturday, Donald Trump promised to impose a wave of tariff surcharges on several of his European allies, starting at 10% from February 1, and rising to 25% from June 1, until the United States secures Greenland.

In response, Ursula von der Leyen stated that the European Union stands fully in solidarity with Denmark and warned that new tariffs could jeopardize transatlantic relations.

According to Bloomberg, the EU is considering imposing tariffs on some $93 billion worth of American products in retaliation, raising serious concerns about the return of a trade war between Washington and Brussels.

"However, we advise investors to remain calm," tempers Joachim Klement of Panmure Liberum, judging that these surcharges could be easily circumvented by affected companies.

"European manufacturers simply need to route their products to the United States via countries exempt from these surcharges, such as Spain, Italy, Belgium, and Ireland," explains this market analyst.

Against this backdrop, operators are paying little attention to good news on the inflation front in the eurozone: Eurostat has revised its annual rate down to 1.9% for December, compared to a flash estimate of 2% and after 2.1% in November.

Still on the macroeconomic data front, the week will be marked in the United States by the release of a new estimate of third-quarter GDP, as well as household income and spending figures, accompanied by the PCE price index.

On this side of the Atlantic, the coming days will see the publication of the ZEW indices in Germany and the business climate index in France, as well as inflation in the United Kingdom and flash PMI estimates.

The week will also see the earnings season gather pace, notably with results from Netflix, 3M, J&J, Travelers, P&G, and Intel in the United States, as well as Rio Tinto, Mercedes-Benz, LVMH, and Ericsson in Europe.

For now, on the CAC40, luxury stocks like LVMH (-4%) and Hermès (-3%) are bearing the brunt of the renewed trade tensions, while Thales (+2%) appears to be benefiting from the hardening of Euro-American relations.

Elsewhere in Europe, Bayer is up 7% in Frankfurt after the U.S. Supreme Court agreed to hear the Durnell case, which set a precedent for compensation for damages caused by Roundup, a huge issue for the German group.

D'Ieteren jumped 8% in Brussels, following a rumor reported Friday evening by the Financial Times that its subsidiary Belron (parent company of Carglass) is in preliminary discussions regarding a potential stock market listing.