The US president has declined to unequivocally back the alliance's collective defense obligations

US President Donald Trump has refused to publicly affirm that he would unconditionally defend America's allies under NATO. He made the remarks on Tuesday en route to the NATO summit in The Hague.

Under Article 5 of the North Atlantic Treaty, NATO members must treat an attack against one of them as an attack against them all.

Asked by a reporter if he was committed to Article 5, Trump replied, "Depends on your definition."

"There are numerous definitions of Article 5. You know that, right? But I'm committed to being their friend. You know, I've become friends with many of those leaders," he added.

When asked to clarify his position aboard Air Force One, the president said, "I'm committed to saving lives. I'm committed to life and safety. And I'm going to give you an exact definition when I get there."

NATO Secretary General Mark Rutte, for his part, told reporters that he has "no doubt that the US is totally committed to NATO, totally committed to Article 5." Rutte recently sent a glowing letter to Trump, praising his "decisive action in Iran" and promising "another big success" at the summit in The Hague.

Trump, who has at times spoken disparagingly about the alliance, has long urged members to boost their defense spending. He broke ranks earlier this year by reviving direct talks with Russia and refusing to offer the kind of unconditional support for Ukraine that it enjoyed under his predecessor, former President Joe Biden.

The change in US policy prompted European NATO members to consider moving away from reliance on Washington for their defense. German Chancellor Friedrich Merz said this week that Europe can't afford to "free ride" on US security any longer. In April, French President Emmanuel Macron stated that Europe must acknowledge it will not be "a geopolitical priority" for the US in the coming years.