Russian President Vladimir Putin at a meeting in Moscow, Jan. 6.

Photo: Mikhail Klimentyev/Zuma Press

World War II revisionist historian Phillips O’Brien has been fighting the good fight lately on Twitter, upholding the thesis of his 2015 magnum opus, “How the War Was Won.” To wit, Russia’s contribution to victory in the world war was relatively minor after all. German weapons and materiel consumed in battle on the eastern front calculate out to a modest fraction of those destroyed or prevented from being created by the Western air and naval war against Germany’s productive capacity.

He turns on its head an old belief that allied bombing was ineffective because Nazi production for a time continued to grow in absolute terms. Mr. O’Brien suggests the effect on potential output is what matters. The Germans apparently agreed. According to Mr. O’Brien’s figures, the lion’s share of resources went to the Luftwaffe and German navy even at the height of the ground campaign in the east.

Russia today possesses a small fraction of NATO’s productive capacity and will not be able to make up the gap, never mind neither’s being under direct military threat. One close similarity with Hitler, however, is the disappearance of any prospect of gain from the war Mr. Putin started in Ukraine, which offers now only variations on loss and disaster. The war continues only to spare Mr. Putin a loss of face from admitting a truth that is obvious to 100% of the people around him.

Which brings us to the question of negotiations, faintly in the air since the prisoner trade for a U.S. women’s basketball star in early December. Mr. Putin desperately needs talks if they can get him out of the mess he created. They can’t. He waited too long and now it appears nothing can seriously alter the outcome.

By the same token, if you were Ukraine’s president and able to play a subtle game, you might actually sign a cease-fire that concedes for now a Russian presence on Ukrainian soil with a certain jaunty confidence. That’s because, from the moment the shooting stops, your economy, your military capacity, your social cohesion go straight up, kindled not only by a powerful sense of victory and national achievement, but by an in-pouring of U.S. and European aid seeking to share the victory and express gratitude for the peace.

Nothing as good happens for Mr. Putin when the shooting stops. It becomes obvious the relative power of the two countries is on a permanent trajectory to Russia’s detriment. Western sanctions will be rolled back slowly if at all. The hard-hearted leaders of China aren’t going to save the day, pouring in resources to sponsor Russian revival; they will certainly find ways, however, to exploit and take advantage of Russia’s weakness.

Ending the war would be a blessing to the Russian people and Mr. Putin’s budget, but it would crystallize Russia’s status as a ramshackle power. Russia’s relations with Ukraine would be inverted overnight—Russia would be the supplicant, seeking support for sanctions relief. Ditto Moscow’s relations with other states along its periphery. Its intrinsic vulnerabilities would be thrown into relief: its backward and shrinking population, its unwieldy geographic expanse, its shaky imperial rule over distant and diverse populations who have no reason to love Moscow.

The Russian Federation would be seen anew through the prism of Ukraine’s national rise—as a federation that only holds back the development of its people and prevents them from having prosperous relations with the West.

The ironies can’t be lost on anyone. If Mr. Putin had stuck with his mobilization on Ukraine’s borders and not invaded, we might still be thinking of Russia as a great power with a formidable conventional military. The blame-NATO argument might yet carry some weight. Now, if NATO provoked the war, it only provoked Mr. Putin to an act of self-destruction, as he seems implicitly to acknowledge. All his familiar and conflicting justifications have taken a back seat to insisting he had “no choice” because if he had a choice he made a terrible one.

His loudest partners at home, such as Wagner Group’s Yevgeny Prigozhin, clearly see the abyss opening beneath their feet, the end of imperial Moscow. How exactly the war might yet play out is far from certain but the world now knows, in the process, it will be managing the demotion of Russia from putative great power to the sick man of Eurasia.

In all this, a wild card isn’t China so much as Germany, which understandably fears chaos. Russia and its sympathizers in the West already are softening sanctions wherever the rest of us aren’t looking, such as allowing Russia’s coal exports to bounce back to their highest level ever. And yet the psychological reality of Russia’s defeat seems likely to be so impressive that even Germany will have a hard time finding a constituency to soften Russia’s fall as much as some would like.