Trump says he will “encourage” Russia to do “whatever the hell it wants” with NATO allies that do not pay for defense. Secretary General of the Alliance, Jens Stoltenberg, has accused the Republican presidential candidate of “undermining the security” of member countries.

Trump's comments plunge the Alliance into a US election campaign overflowing with animosity. They have reopened uncertainty in Europe about the future of a key institution in post-war transatlantic relations.