NATO Secretary General Jens Stoltenberg walks out to speak to reporters after meeting with President Donald Trump at the White House.Jonathan Ernst / Reuters

Donald Trump has said it is obsolete, Emmanuel Macron argues it is suffering a “brain death,” and fewer than a third of people in Germany, France, and Spain have a favorable view of it. Questions abound over its long-term relevance; its own members are placing tariffs on one another; and through it all, Russia looms as the ever-present adversary. As leaders of NATO’s 29 member states meet in London to mark its 70th anniversary, the military alliance faces a wide array of critics and challenges.

It seems an impossibly long and difficult set of issues, certainly not ones well suited for a former anti-war activist, someone who once opposed his own country’s membership in NATO. Yet that is precisely who is at the organization’s helm.

Meet Jens Stoltenberg—the unlikely leader who may well be doing more than anyone else to hold NATO, and the West, together.

First appointed NATO secretary-general in 2014, Stoltenberg will soon become the longest-serving head of the alliance in 35 years: Since a former head had to be quietly forced out in the mid-’80s, the organization’s leaders have conventionally been limited to one four-year term, plus a one-year extension should the alliance choose to exercise it. For Stoltenberg, that means he should be in his last year on the job. In March, however, NATO member states agreed to extend his term as the group’s top political official for two more years, taking him to September 30, 2022.

The reason? NATO’s chief internal critic: Trump.

According to two senior British officials, one current and one former, who spoke on condition of anonymity to discuss NATO’s internal politics, the organization’s European members were desperate to avoid instability before next year’s American election. They worried that any change to its leadership would mean giving Trump, as leader of NATO’s most important power, considerable sway over Stoltenberg’s successor. By handing Stoltenberg two more years, the organization had bought itself breathing space beyond the 2020 election, when a new president may be in the White House.

Still, the move exposes the structural weaknesses at the heart of the alliance, suggesting that NATO feels unable to appoint a new leader, fearful of exacerbating its internal tensions.

Stoltenberg has repeatedly tried to attribute the fissures within NATO—from Trump’s regular complaints about the defense-spending contributions of its members to Macron’s diagnosis—not to its own inherent fragility, but to the realities of being both a political and military alliance.

“We are 29 allies from both sides of the Atlantic,” Stoltenberg told a conference in London yesterday. “It would be strange if 29 allies with different political parties, different histories, [and] different geographies always agreed on everything. The lesson we’ve learned from history is that despite these differences, we have always been able to unite around our core task to protect and defend each other, because it’s in our international security interest to do so.”

Stoltenberg’s commitment to dialogue and compromise has served him well in his time as secretary-general, and indeed endeared him to NATO states when he was first tapped for the job.

Born to a family of politicians and diplomats, his entry into politics came early in life with his opposition to the Vietnam War as a teenager. In his mid-20s, he became the leader of the youth wing of Norway’s Labour Party, which opposed Norwegian membership in NATO (a position that Stoltenberg shared at the time, but later helped reverse). He eventually became the country’s prime minister and by 2014, after serving three terms in the position, he had distinguished himself not only as a firm supporter of the alliance (his government backed NATO military campaigns in both Afghanistan and Libya), but as a skilled diplomat—particularly when engaging with Russia. In 2010, while still Norway’s leader, Stoltenberg struck an agreement with Moscow to resolve a decades-long dispute over maritime borders in the Barents Sea, a breakthrough attributed in part to his rapport with then-President Dmitry Medvedev.

“He comes from a country that has had the Soviet Union and Russia as a neighbor forever,” Jan Egeland, the former United Nations undersecretary-general and a longtime friend of Stoltenberg’s, told The Atlantic. “That’s the political reality he grew up with … so he’s actually uniquely qualified. NATO would perhaps be in another place, in a much worse place, if someone else had been at the helm for the last few years. And it’s because of his mentality, because of his background, because of his skills, ability, and wisdom, and enormous diplomatic ability.”

Stoltenberg’s ascension came at an unstable time for the military alliance. By October 2014, Russia’s seizure of Ukraine’s Crimean peninsula was only months old, and the alliance’s years-long military presence in Afghanistan was winding down. In 2019, Russia’s hold on Crimea remains firm, the situation in Afghanistan remains uncertain, and new challenges for the alliance have emerged: the crisis in northeast Syria, a rising China, and growing threats surrounding cybersecurity and climate change.

And then there are the internal divisions among NATO members themselves, which, for the purposes of this gathering, have been under particular scrutiny. Already, Trump has criticized Macron for his “brain death” remarks; Turkish President Recep Tayyip Erdoğan has said Ankara would oppose NATO’s plan for defense of the Baltics if the alliance failed to recognize organizations Turkey deemed to be terrorists; and the host, Britain, is worried that the American leader will wade into its domestic politics, ahead of next week’s election. (Stoltenberg, through a spokesman, declined to be interviewed for this story.)

Stoltenberg’s job, in effect, is “like herding cats,” Egeland said, noting that while the secretary-general must represent NATO’s policies, he also has to consider the constraints placed on NATO leaders as well. “All international policies are … informed by the domestic policies, so it will be tough.”

Though European states were keenest to keep Stoltenberg in place, it also speaks to the Norwegian’s leadership and respect within NATO that the United States agreed to have him stay on. Even Trump, who is not shy about criticizing the alliance and its members, appears to have been won over.

Stoltenberg has put a lot of work into reassuring Trump that the United States’ allies were increasing their military expenditures toward the goal of 2 percent of GDP a year on defense—a persistent stipulation of American presidents but one Trump has forcefully demanded, often in undiplomatic terms. During a 2017 trip to the United States, the NATO leader even gave an interview to Fox News crediting Trump’s pressure for increasing European countries’ military spending by $100 billion. On that same trip, the American president declared NATO was “no longer obsolete.”

Following a bilateral breakfast meeting in London yesterday, Trump lauded Stoltenberg for doing “a very good job in running NATO” and bringing the alliance together. He even appeared to attribute his change of heart toward the alliance to Stoltenberg.

“When I came in, I was angry at NATO,” Trump told reporters in London, saying that the pair had worked together to increase how much other countries were spending on their militaries by $130 billion, an apparent reference to the rise in defense expenditure over the past five years.

At one point, referring to Stoltenberg, the U.S. president said, “I think he is doing a fantastic job; I am a big fan.”

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