There is a scenario in which Russia corrects course, but no one inside or outside Russia believes that will happen as long as Vladimir Putin is President. If Putin could be deposed by the Russian people--or more plausibly by military leaders--then Russia could, if not forswear corruption and kleptocracy, at least confine its violence to its own borders. Before long, Russia could even rejoin the global economy.

That is not likely. Vladimir Putin is surrounded by what amounts to a private army, loyal and well-paid, and behind that another legion of bloodthirsty mercenaries. To the fortunes of his oligarch cronies, add his own estimated $250 bn in stolen and stashed assets. The conditions for coordinating a palace coup simply do not exist at this time.

If Putin stays, then Russia will not back down from the invasion of Ukraine. Sanctions won't stop him; China will keep Russia's economy treading water; that is enough. Ukrainian soldiers and citizens are putting up an incredible fight, but the outcome is a foregone conclusion: Russia has air superiority, and Putin spares no scruples for civilians, so Russia will win the war.

Then begins the occupation. Already, the death toll is in the thousands and there are at least a million refugees. The degree of violence required to continue suppressing the spirited and steadfast people of Ukraine would be extraordinary. Ukrainians have come too far in the past 30 years to let their freedom slip away: they simply will not tolerate Russia's presence in Ukraine, in any form.

Perhaps our Western leaders are thinking, If the conflict in Ukraine is drawn out long enough, Russians themselves will tire of the project and Putin will have to return to barracks. The Russian military will become threadbare with exertion, its leaders more inclined to turn their guns on the Kremlin than Kyiv.

Perhaps; but in the interim I am afraid that grotesque violence--on the scale of ethnic cleansing--is the price that Putin is prepared to exact on Ukraine. In the meantime, Russian forces will become entrenched in Ukraine's cities. It would be easier in the long run to keep them from gaining a foothold than trying to remove them much later.

Is it necessary to allow such events to unfold before intervening; or should we intervene now? Intervening would undoubtedly make us co-belligerents, but as long as we stay out of Russian airspace and off Russian soil, there is no reason for Russia to come across NATO's borders. Were Russia to boldly attack a NATO country within its territory, the Russian military must know the response would be terminal for the Russian state.

In hindsight, we should have done more in Rwanda, South Sudan and Yemen; we should have stayed out of Iraq and Afghanistan. We should have been more circumspect at Versailles, in 1919; we should have stopped Germany in 1938, before Sudetenland. We should have embraced a democratic Russia in the 1990s and incorporated it fully into the rules-based system and the international security apparatus, instead of humiliating or ignoring it.

It is easy to understand how all that hindsight is contributing to our paralysis at this moment of reckoning, but it is that: NATO member or not, Ukraine is an imperfect but functioning democracy, as good as has been produced since the fall of the Iron Curtain. Allowing Russia to erase Ukraine will do lasting damage to democracy as an ideal.

We are approaching another, more terrible day of reckoning, and we need to establish a precedent now that we can confidently follow on that dark day: the day when China comes for Taiwan. That will not be a day for hand-wringing and sanctions but a day to act forcefully with unity. The war for Ukraine is the dress rehearsal, and the future of democracy depends on our response.

We must turn back Russia's invasion, but go no further. We should begin by enforcing a no-fly zone over Ukraine. We do not need to decapitate Putin's regime, only give Russians themselves the space to swing the axe. We absolutely do not want to make a project of Russian regime change or democracy building.

Yet we must simultaneously allow space for Russia to rejoin the rules-based international order and the global economy, under clear and achievable conditions which we are prepared to support with the same solidarity that we are prepared to defend Ukraine's sovereignty. Russians must be made to understand that the West wants a sovereign, prosperous and peaceful Russia to be part of the system, not apart from it.

The analogies to chess are inapt: Putin is not playing chess, he is making a simple bet. He has bet all of Russia's chips that the West will not sacrifice blood for a fragile democracy on its margins. Bluffing with sanctions is not going to work. Only an overwhelming show of military support for Ukraine designed to drive Russia back to her borders will settle it.