How far will Vladimir Putin go to avoid an abject humiliation in Ukraine? Chatter on that question has focused on a Russian doctrine of “escalate to de-escalate,” which would force concessions or surrender by making the war so horrid that a Russian victory becomes the safer option. Putin has to some extent already begun using E2D by indiscriminately bombing civilian areas — but Ukrainian resistance has instead stiffened, and so has the spine of the West.

Putin has hinted for weeks that NATO’s support for Ukraine could result in the deployment of tactical nuclear weapons to up the ante for some sort of concessions. Now that the unthinkable has suddenly become thinkable, former national-security director Robert C. O’Brien writes at the Wall Street Journal, the US and its allies need to act now to discourage Putin from even attempting such a move:

If Ukrainian forces push Russia out of the Donbas and even Crimea, there would be no way for Mr. Putin to hide Russia’s humiliating loss from its people. If such an outcome became likely, would he use one of his thousands of “tactical” or “battlefield” nuclear devices to take out Kharkiv, Odessa or even Kyiv in an attempt to save face and end the war on terms he dictates? This possibility is surely on the minds of President Biden’s national security adviser, Jake Sullivan, and his staff.

The time is now to deter Russia from “escalating to de-escalate.” The U.S. must unambiguously communicate to Moscow what lies ahead if it goes down this terrible path. Mr. Putin and his supporters need to understand that if he detonates a nuclear weapon in Ukraine, the U.S. response will be swift and significant—far exceeding the limited export sanctions under consideration around the world in response to Russian atrocities in Bucha.

O’Brien suggests a range of options, none of which involve the use of nuclear weapons, in either pre-emptive or retaliatory fashions. In fact, none of them explicitly involve military action, although the first two would likely require it:

• Clear the Russian navy’s two remaining Slava-class cruisers, their escort ships and submarines from the Mediterranean. This could be accomplished by a diplomatic démarche followed by more-forceful action if necessary to enforce compliance.

• Eliminate Russian air and military assets in Syria and Libya on the same basis. The U.S. and the North Atlantic Treaty Organization have the ability to do so fully within hours if Russia refuses to withdraw its forces to its homeland.

Putin’s not going to pack up those forces and send them home. The only way to accomplish this is to sink all the ships and destroy all of Russia’s other forces in the Mediterranean. That would be an act of actual war, and Putin might even welcome that as a vindication of his propaganda that Ukraine isn’t the entity kicking his ass, but that Russia is actually fighting NATO in Ukraine.

If we’re contemplating direct military action — and we’d better be damned sure that’s what we want to do first — there’s a more effective way to punish Putin for threatening nuclear weapons use. Rather than attack surface ships, the US should make it clear that any movement of Russian nuclear arms will be seen as an existential threat to NATO and a clear violation of a number of agreements intended to keep peace in Europe and around the world. At that point, the most existential of those threats would be the Russian boomers — the missile-launching submarines that could deliver nuclear attacks on the US and our allies within minutes.

If Putin moves his tactical nukes, every one of those boomers should rest on the ocean floor within minutes. We shouldn’t specify that as a response, and in fact we shouldn’t even officially discuss it. But if Putin wants to use his nuclear arsenal in a game of poker, then we should take immediate action to make sure he can’t place his best bet. It would demonstrate an end to the idea of symmetric response, plus very specifically target Russia’s nuclear forces rather than just the broader military.

Plus — and this is where the plan would be strategic — it might never really come to light. If we don’t discuss it, Putin would have to admit losing his advanced missile submarines to NATO despite decades of Russian insistence on competitiveness in naval warfare. The very prospect of that humiliation might deter Putin from escalating in a nuclear fashion, especially given the incompetence already demonstrated in both his army and his navy against Ukrainian forces.

What’s much more likely to happen, though, is that we’ll dither on escalating sanctions instead while hoping Putin’s not that crazy. Perhaps he’s not, but that’s what we thought before he invaded Ukraine in the first place. It’s time to start making Putin worry about what we might do rather than the other way around.