“Deterrence is in the mind of our adversaries. We should not leave (any) room of miscalculation or misunderstanding in Moscow about our readiness, our commitment and our resolve to protect all allies,” the Secretary General said on Wednesday ahead of a meeting in Brussels of the alliance’s defence ministers.

“And the reason to do so is not to provoke a conflict but to prevent a conflict as NATO has done successfully for the 65 years.”

Keeping NATO strong is in “the national interest of the United States,” he added, as the country “has never fought a war alone.”

Stoltenberg’s caveat comes days after Trump, who is running again for president and is currently the Republican frontrunner, suggested in a South Carolina rally he would “encourage” Russia to attack any NATO nation that does not meet the target of spending 2% of gross domestic product (GDP) on defence.

He claimed the leader of an unnamed “big country” in Europe had asked him: “If we don’t pay, and we’re attacked by Russia, will you protect us?”

Trump said his response was: “No I would not protect you. In fact, I would encourage them (Russia) to do whatever the hell they want. You gotta pay. You gotta pay your bills.”

The remarks sparked an immediate outcry and drew fierce condemnation from allies, who saw it as an imprudent disregard of Article 5 of collective defence at a time of war in Europe. US President Joe Biden did not mince words, calling Trump’s comments “dumb,” “shameful,” “dangerous” and “un-American.”

“Can you imagine a former president of the United States saying that? The whole world heard it,” Biden said earlier this week. “The worst thing is, he means it. No other president in our history has ever bowed down to a Russian dictator.”

German Chancellor Olaf Scholz said Trump’s remarks had been “irresponsible and dangerous,” while European Council President Charles Michel spoke of “reckless statements” that “serve only Putin’s interests.”

During his tumultuous four years in office, Trump often portrayed NATO as a transactional enterprise based on countries chipping in money rather than a military partnership founded on mutual trust and cooperation. With polls predicting a close presidential race, Trump’s incendiary comments ratcheted up long-harboured fears that his possible return to the White House might lead to America’s withdrawal from the alliance, which would leave Eastern Europe exposed to Russian aggression.

“The whole idea of NATO is that an attack on one ally will trigger a response from the whole alliance. As long as we stand behind that message, together, we prevent a military attack on any ally. So the purpose of NATO is to prevent war, to preserve peace,” Stoltenberg told reporters when asked about Trump’s comments.

“So any suggestion that we’re not standing up for each other, that we’re not going to protect each other undermines the security of all of us, increasing the risks,” he went on. “It’s important that both in actions and in words we communicate clearly that we stand by NATO’s commitment to protect and defend all allies.”

First agreed in 2006, the pledge of NATO allies to spend 2% of their GDP on defence is a shared objective, rather than a legally binding obligation. 

The target has been reaffirmed several times over the years and became a minimum requirement in the wake of Russia’s all-out war in Ukraine. European governments have since then announced national plans to rapidly ramp up their defence spending, although as of 2023, only 11 of the 31 allies met the 2% target.

On Wednesday, Stoltenberg revealed that, according to the alliance’s latest estimates, up to 18 allies will reach the objective by the end of 2024. European allies and Canada are expected to invest $380 billion in defence.

“The criticism (in the US) is not primarily about NATO. It’s about NATO allies not spending enough on NATO. And that’s a valid point,” he said.

“This message has had an impact. European allies and Canada have stepped up and I count on them to continue to do so.”