At the heart of NATO, the world’s longest-standing security alliance, is the notion that an attack on one is an attack on all. But with many in Europe doubting a Trump-led United States will really come through for them,

President Macron has aired the idea that France's deterrence force could be used to defend of other European countries.

We simply must become stronger together in nuclear deterrence in Europe,' Merz, expected to become Germany's next chancellor, said in an interview as the continent seeks to respond to US President Donald Trump's upending of the transatlantic alliance.