We should not delude ourselves about how far Mr. Putin could go. Since the outbreak of the war, he has been cracking down in Russia—closing the last remnants of a free press, arresting critics and tightening the laws against protest and dissent. But the Soviet era saw much more totalitarian controls and much greater terror than anything that exists in Russia today.

Would Mr. Putin rebuild the Gulag Archipelago and re-create the terror through which Stalin ruled Ukraine? If the alternative is to flee Moscow in disgrace and pass the remaining years of his life as a state pensioner in China, he will almost certainly move in that direction. Mr. Putin cemented his hold on power by deploying ruthless violence against civilians in Grozny to crush the Chechen drive for independence. Why would he yield power without using every available method to hold on?

The question is whether he can succeed. On the one hand, Mr. Putin’s state and the Russian bureaucracy today lack the ideological commitment and the experience of civil war that made Stalin’s Communist Party such an effective instrument of mass repression and terror. Today’s security agency, the FSB, is less powerful than the KGB, much less is it a match for the NKVD of Stalin’s time. There is also a question of how far into the darkness Mr. Putin’s allies are ready to travel with him.