Come July, NATO allies will gather in Vilnius for their second summit since Russian President Vladimir Putin launched his genocidal war of aggression against Ukraine. There’ll be 31 of them this time, after Finland joined the club in direct response to Putin’s bellicosity. What should they decide?

One way or another, every discussion will touch on Putin. The neo-Tsarist, imperialist, irredentist and atavistic threat he represents menaces not only non-NATO countries such as Ukraine or Moldova but also NATO allies including Estonia, Latvia and Lithuania. And while some items on the Vilnius agenda may seem uncontroversial, others pose dilemmas that could prove fiendish -- depending on the success or failure of Ukraine’s expected “spring offensive.”

The easiest category should be resources. NATO needs more. So the allies should reach a binding agreement to spend at least 2 percent of gross domestic product on their militaries. NATO must also have more say where that money goes. One country might be told to build fewer submarines, another to invest more in fighter jets, and so on. The goal must be to face eastward toward the Kremlin not as a ragtag horde, but as one coherent and coordinated fighting force.

More fundamentally, the allies should formally ditch their old strategy of deterrence by “punishment” or “retaliation.” That model assumed that in the event of a Russian attack, the enemy would initially conquer swathes of NATO territory. Then, however, the US and other allies would ride to the rescue, liberating friends and expelling Russia with overwhelming force.

Perhaps counterintuitively, deterrence by retaliation made more sense in the relatively pacific zeitgeist of the preceding era, symbolized by the NATO-Russia Founding Act of 1997. Its premise was that Russia and the West “will build together a lasting and inclusive peace” based on “mutual trust and cooperation.” Russia pledged to behave itself in eastern Europe, and NATO promised not to deploy large forces or scary weapons in its eastern member countries to avoid threatening or provoking the Kremlin. That also meant the allies couldn’t have stopped a surprise Russian onslaught even if they’d wanted to.

Putin unilaterally destroyed the basis for that NATO thinking. First, he wantonly abandoned the Founding Act when he seized Crimea in 2014 and invaded the rest of Ukraine in 2022. Second, his troops, by committing atrocities in Bucha and other Ukrainian territories they overran, demonstrated what would await Balts, Poles or Finns while waiting to be liberated by the rest of NATO. Deterrence by retaliation alone is no longer enough.

So NATO should explicitly subscribe to “deterrence by denial.” That’s jargon for defending “every inch” of NATO territory, starting with the first -- that is, stopping the Russians before they occupy any territory. To make this kind of deterrence credible, NATO must have awe-inspiring forces not just in the rear -- at US bases and nuclear silos in Germany, for instance -- but at the front.

After Putin seized Crimea, the alliance took a baby step in that direction, with a so-called “Enhanced Forward Presence.” It consists of four multinational battlegroups, in Estonia, Latvia, Lithuania and Poland. Last year, the alliance added another four -- in Bulgaria, Hungary, Romania and Slovakia.

But these deployments rotate soldiers in and out, and are by design small. That was part of the old rationale of trying not to provoke Putin -- which he has made obsolete by becoming a paranoid and resentful aggressor with or without provocation. So NATO’s forward presence must become a permanent fighting force, with whole brigades instead of mere battalions, each armed to the teeth.

That raises the radioactive question of nukes. Since his invasion, Putin has repeatedly breached nuclear taboos by threatening tactical strikes. Just the other day, he upped the ante again when he said he’d station nukes in his neighboring state of Belarus.

NATO must demonstrate to Putin, as to his possible challengers within Russia and copycat dictators elsewhere in the world, that it will never tolerate such nuclear intimidation or blackmail. Otherwise, Putin will keep at it, and other regimes will race to get their own warheads and copy him. The world would become a nuclear matchbox.

NATO should therefore announce plans to follow any nuclear proliferation by Putin. If he puts warheads in Belarus, NATO would place its own in the Baltic countries or Poland.

The most agonizing question concerns Ukraine. Ambiguity about its future inside or outside of NATO has been a factor in tensions between Russia and the West at least since 2008, when the alliance said that Ukraine and Georgia “will become members” -- but at some undefined time in the future. That left Kyiv one-quarter in and three-quarters out, while letting Putin spin his narrative that the West is bent on encircling Russia.

Today, there are strong arguments for admitting Ukraine. After the war, it will need security guarantees from the West anyway. And the prospect of membership will add to Ukrainians’ morale as they fight for their national survival.

That said, the case is stronger against extending Article 5 -- the mutual-defense clause -- to Ukraine. One consideration in weighing NATO expansion should be whether the potential member would make the alliance stronger or weaker. This may not have been top of mind in 2017 when Montenegro joined -- but that was before the zeitenwende of Putin’s invasion. Finland does make NATO stronger, as will Sweden whenever it joins. Ukraine would not.

Promising to admit Ukraine to NATO, moreover, would compromise another imperative. The US and its allies must never dictate to Kyiv its objectives in defending itself, or the terms of peace negotiations. But if all the allies were pledged to protect Ukraine, their fates would be intertwined, and NATO might “sleepwalk” into World War III, depending on Kyiv’s choices. To avoid that, the West would have to interfere in Ukraine’s decisions.

To some extent, of course, the destinies of Ukraine and Europe already are tied together. That’s why the West must support Ukraine with everything it’s got, short of Article 5. Beyond that, the best NATO can do is to leave no doubt in Moscow that any attack on any ally would lead to certain Russian defeat.

Andreas Kluth

Andreas Kluth is a Bloomberg Opinion columnist covering European politics. -- Ed.

(Tribune Content Agency)