Trump has time and again criticized member countries of the alliance that have failed to hit a target, agreed in 2014, to spend 2 percent of their gross domestic product (GDP) on military forces.
The bond between Western countries is already under stress following June’s G7 summit in Canada, when Trump criticized the leaders of Germany and Canada over trade deals.
At that G7 meeting, Trump also claimed that NATO was “much too costly for the U.S.” and has since written to NATO leaders urging them to accelerate their outlay.
The man in the middle of the debate is NATO Secretary-General Jens Stoltenberg.
He told CNBC’s Hadley Gamble on Thursday that the alliance was moving in the right direction and that President Trump recognized that.
“The good news is that we have started to do exactly that and we have started to see a significant increase,” Stoltenberg said. ”Over the past few years we have added $87 billion from Canada and the European allies and that makes a real difference.”