> European leaders were already uncertain whether Mr Trump would honour the alliance’s Article 5 clause – which states that a military attack on one ally is con

> European leaders were already uncertain whether Mr Trump would honour the alliance’s Article 5 clause – which states that a military attack on one ally is considered an attack on all – and come to their aid. Article 5 has only ever been invoked once in NATO history. It was invoked by America. NATO allies came to America's aid: https://en.wikipedia.org/wiki/North_Atlantic_Treaty#Article_5 https://en.wikipedia.org/wiki/North_Atlantic_Treaty#Article_...