As the NATO summit in The Hague kicks off amid growing geopolitical tension, US President Donald Trump has once again stirred controversy-this time by casting doubt on one of the alliance’s foundational principles: Article 5, the mutual defense clause. When asked by a reporter during his flight aboard Air Force One whether he remained committed to the article’s promise of collective defense, Trump gave a characteristically evasive and provocative reply: “Depends on your definition.”

“There are numerous definitions of Article 5. You know that, right?” Trump said. “But I’m committed to being their friend. You know, I’ve become friends with many of those leaders.”

His comments have triggered anxiety among NATO allies and renewed long-standing concerns about Washington’s reliability as the cornerstone of European defense. While Trump attempted to soften his stance by adding that he is “committed to saving lives” and promising a “definition” at the summit, the ambiguity surrounding his words has already fueled speculation about the US’s future role in NATO.

Article 5 of the North Atlantic Treaty is NATO’s bedrock principle. Invoked only once in the alliance’s history-after the September 11 attacks in 2001-it obliges all member states to consider an attack on one member as an attack on all. For decades, this collective security guarantee has served as a deterrent to potential aggressors and a symbol of transatlantic solidarity.

By publicly suggesting that the article is open to interpretation, Trump has disrupted this consensus. His........

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