A mural on a restaurant wall in Vilnius, Lithuania’s capital, depicts Donald Trump and Russian President Vladimir Putin kissing. (Petras Malukas/AFP via Getty Images)

In tapping retired Lt. Gen. Michael Flynn to serve as his national security adviser, President-elect Donald Trump has chosen someone who proudly claims to have shaped the next president’s views that NATO is “obsolete” and that the United States should threaten not to come to the defense of NATO member states if they don’t pay their fair share.

Flynn told ABC News in May that he first spoke to Trump in September 2015: “We did talk about NATO and I told him . . . the United States — we pay too much of the bill. NATO is a 20th-century model and needs to be retooled for 21st-century threats that we collectively face, you know cyber is one of them. So, I said those things to him when we first talked.”  He added, “I don’t have any problems with what [Trump] said about NATO. And if it’s to put NATO on alert, to say, hey, NATO, we got to figure this out — this is no longer the Cold War — we need to organize ourselves differently. And, frankly, if you are part of the club, you’ve got to pay your bill, and for countries that don’t pay their bills, there has got to be some other penalty.”

American officials have complained about their NATO allies before

Flynn won’t be the first U.S. official to urge Europeans to contribute more to the collective defense. After all, in his last major address in Europe before leaving office in 2011, then-Defense Secretary Robert Gates stated, “The blunt reality is that there will be dwindling appetite and patience in the U.S. Congress, and in the American body politic writ large, to expend increasingly precious funds on behalf of nations that are apparently unwilling to devote the necessary resources . . . to be serious and capable partners in their own defense.” Although polls consistently show that an overwhelming majority of Americans view NATO as essential to U.S. security, Trump during the campaign suggested that those allies that didn’t pay sufficient amounts would not be able to rely on the United States to protect them, thereby undercutting the core of NATO, its famous Article 5.

Article 5 is at the core of NATO’s commitments

In the 1949 Washington Treaty that established NATO, Article 5 stated, “The Parties agree that an armed attack against one or more of them in Europe or North America shall be considered an attack against them all.” As Flynn suggested, it was designed against a 20th-century threat: a Soviet land offensive in Europe. The core function of NATO was to provide confidence that the United States would come to the aid of its Western European allies, reassuring them and forestalling possible Soviet invasion. In addition, NATO addressed European fears that Germany might rise again to threaten its neighbors. This underpinned economic prosperity in Europe, in turn strengthening the U.S. economy and global position.

After the Cold War, NATO struggled to find a role

Arguments about NATO’s obsolescence are not new; they began as soon as the Soviet Union collapsed. By then NATO had grown to 16 members that no longer faced a Russian military threat. But NATO enabled the United States to dominate European security affairs for four decades. Officials in the George H.W. Bush administration didn’t want to lose that standing, particularly as the European Community, which excluded the United States, was forming a closer union. Europeans, meanwhile, had grown dependent on the U.S. provision of security, and many were still nervous about the newly unified Germany. In the United States, both Democratic and Republican administrations supported enlarging NATO to include the countries of Central and Eastern Europe so as to spread the prosperity and peace of Western Europe across the continent.

Since the end of the Cold War, the alliance has gone to war not to defend a member state from armed attack but for the purpose of humanitarian intervention, first in Kosovo in 1999 and later in Libya in 2011. After the Cold War, the closest NATO came to acting as originally envisioned was in the aftermath of the terrorist attacks in the United States on Sept. 11, 2001. Indeed, for the first and only time in its history, NATO members invoked Article 5.  Contrary to the expectations of 1949, when Article 5 was supposed to ensure that the United States would come to the aid of its allies in Western Europe, in 2001 the European members of the alliance offered to come to the defense of the United States.

The administration of George W. Bush, however, chose not to accept the offer of support from alliance members, because it had found the NATO operation in Kosovo cumbersome. Instead, the administration opted to assemble a U.S.-led “coalition of the willing,” in which the United States would work with a few select allies to pursue al-Qaeda in Afghanistan — rather than through NATO. Article 5 was used only to organize a maritime counterterrorism operation in the Mediterranean, known as Operation Active Endeavor.

After the United States became bogged down in Iraq, NATO accepted the Bush administration’s request to assume leadership of the International Security Assistance Force (ISAF) in Afghanistan in August 2003. While NATO was initially responsible for post-conflict reconstruction in Kabul, over time the alliance expanded its operations throughout the countryside. Nearly 50 nations, including Azerbaijan, Finland and the United Arab Emirates, sent troops to Afghanistan in support of ISAF’s mission.

The mission was not without controversy. While participating coalition members like Germany and Italy hailed their countries’ support of ISAF despite their “caveats” restricting military action, U.S. military personnel bitterly joked that the ISAF stood for “I Saw Americans Fight.” The sense of disappointment in NATO as a true alliance clearly predates Trump.

Article 5 became a lot more relevant after Putin invaded Ukraine

There was not much discussion about Article 5 within NATO until Russian President Vladimir Putin invaded Ukraine in March 2014 and declared that Russia reserved the right to protect ethnic Russian populations in neighboring states. Putin believed he could act in Ukraine precisely because his neighbor was not a member of NATO and, therefore, not protected formally by Article 5. But Russia’s intervention also produced anxiety in the Baltic countries and in Poland about the certainty of NATO’s collective-defense commitment. The United States, in particular, has been eager to reassure NATO’s eastern members that the alliance is prepared to defend its member states should Russia threaten them, but Putin had exposed the fact that NATO had done little to plan for this contingency.

NATO used its September 2014 summit in Wales and the one in Warsaw in July 2016 to respond to the threat Russia now poses to the post-Cold War European order. NATO increased sea patrols in the Baltic and Black seas and stepped up its air defense over its eastern territory. The alliance created a small high-readiness rotational force for deployments in the Baltic countries and Poland to deter any Russian aggression.

This has all been thrown into doubt

Trump’s and Flynn’s expressed attitudes toward NATO mean that the U.S. posture toward Article 5 is highly uncertain. While their complaints are not new, their willingness to call NATO’s core commitments into question is unprecedented. Russia has made its aggressive posture toward Europe clear, and its invasion of Ukraine has undermined the bipartisan effort over the past quarter-century in the United States to build a Europe “whole, free and at peace.” The last thing NATO wants is uncertainty regarding the U.S. commitment to Europe. The combination of uncertainty about Trump’s views on NATO and his expressed warmth toward Putin is hugely damaging to policies the United States has followed with bipartisan support for seven decades. Uncertainty may be a great form of leverage in a business negotiation but is disastrous for maintaining a strong alliance. Given the views of Trump and Flynn, those who support the alliance will need to demonstrate its value proposition to the new president or Article 5 will be swept into the dustbin of history.

James Goldgeier is Dean of the School of International Service at American University and author of a 2010 Council on Foreign Relations Special Report on The Future of NATO.