(Bloomberg Opinion) — French President Emmanuel Macron’s doubts about the potency of the North Atlantic Treaty’s one-for-all clause, expressed in his frank interview with the Economist, stem from Article 5’s intentional vagueness. That vagueness, however, is also the greatest source of the commitment’s power — and one reason Vladimir Putin's Russia hasn’t tested it yet.During the drafting of the 1949 treaty, the NATO founders, especially the U.S., strove to avoid any language that would automatically force them to go to war in response to an armed attack against one of them. So Article 5 says only that each NATO country must respond with “such action as it deems necessary.” That leaves a lot of space for legal and political interpretations, discussed at length in a 2019 article by Aurel Sari, an expert on international law at the University of Exeter. He points out, for example, that Dean Acheson, the U.S. secretary of state at the time of the treaty’s signing, thought that an armed attack could mean “the combination of external force with internal revolution.” But the International Court of Justice has ruled since then that providing weapons and logistical support to rebels doesn’t constitute an armed attack, so all an adversary state fomenting a revolution or a secession needs to do is avoid directly controlling the insurgent forces.The legal side of what constitutes an armed attack and what doesn’t leaves a lot of room for actors such as Putin, and his allies like Syrian President Bashar al-Assad, to come up with creative strategies that may or may not rise to the level of threat that would trigger Article 5. If the NATO member on the receiving end asks for help, the others, and above all the U.S., would need to decide whether to respond at all, and then what kind of response is commensurate with the threat.In his interview, Macron mentioned a realistic scenario that would require such decisions. “If the Bashar al-Assad regime decides to retaliate against Turkey, will we commit ourselves under it?” he asked. The retaliation is unlikely to look like a direct Syrian attack on Turkey, which would be suicidal given Turkey’s military superiority. But Assad, helped by Iran and Russia, could stage deniable but deadly attacks on Turkish forces in the border areas they control. When the U.S. triggered Article 5 after the terrorist attacks of Sept. 11, 2001, it was important for the other NATO members that the attack was “directed from abroad.” But what about attacks on Turkish troops in Syria planned from Syria — would they be treated the same?It’s also worth contemplating what NATO would do if Russia decided to foment rebellions similar to those in eastern Ukraine in the areas of the Baltic states with significant Russian populations. Would a putative Narva People’s Republic in Estonia, supplied with weapons and instructors across the Russian border, be considered part of a Russian armed attack or merely an insurgency?Would an uprising in Latvia meant to hand power to the Russian-speakers’ party — which won a plurality in last year’s general election but was again denied a role in the coalition government — qualify for Article 5? Would a more successful Russian-backed coup in Montenegro than the one in 2016 — but an equally deniable one — cut it now that the Balkan country is a NATO member?Russia doesn’t have the resources or the political will to sustain a direct invasion of a hostile country even if there’s no threat of NATO retaliation, as in Ukraine. But rebellions, secessionist movements and coups aren’t out of the question. And then there are high-tech attacks. In August, NATO Secretary General Jens Stoltenberg wrote an article claiming that “a serious cyberattack could trigger Article 5 of our founding treaty.” But what does “a serious cyberattack” mean, and what kind of action would it set off? The U.S. and the U.K. have blamed Russia for the NotPetya ransomware attack, which hit civilian targets including hospitals in the U.S. and Europe and inflicted substantial financial damage, but there was no talk of an Article 5 response afterward. “What will Article 5 mean tomorrow?” Macron asked in his interview, and he’s right that nobody, in the U.S. or elsewhere, can give him a clear answer. That, however, means that Putin doesn’t know the answer, either. For all the doubts that European NATO members would want to go all in for Turkey, or that U.S. President Donald Trump would get into a war with Russia for Estonia or Montenegro, Putin — or, say, Assad — cannot confidently predict that it wouldn’t happen.That uncertainty would be gone if NATO countries clearly specified their red lines. But doing so would be a direct invitation to adversaries to invent and carry out attacks that don’t cross these red lines. The vagueness around Article 5 is a kind of protective shield because in the end, it’s not the legal technicalities that count but the political decisions that NATO members will make, individually and collectively, in any given situation.For that matter, the mutual defense clause in the Treaty on European Union is almost identical to NATO’s Article 5 both in its power and its purposeful lack of precision. By advocating a stronger EU-based defense union, Macron isn’t investing in any stronger security guarantee than the one that exists in NATO. That’s because a stronger one isn’t really possible.To contact the author of this story: Leonid Bershidsky at email@example.comTo contact the editor responsible for this story: Tobin Harshaw at firstname.lastname@example.orgThis column does not necessarily reflect the opinion of the editorial board or Bloomberg LP and its owners.Leonid Bershidsky is Bloomberg Opinion's Europe columnist. He was the founding editor of the Russian business daily Vedomosti and founded the opinion website Slon.ru.For more articles like this, please visit us at bloomberg.com/opinion©2019 Bloomberg L.P.