In recent years, Mr. Navalny’s undeniable leadership of the Russian opposition has also become a kind of sign of President Vladimir V. Putin’s stability. The unchanging leader of the regime is Vladimir Putin; the unchanging leader of the opposition is Aleksei Navalny. It was hard to imagine him being arrested or killed. But everything changes.

If the Russian government has now decided to get rid of Mr. Navalny, that suggests it is constructing some new political configuration in which there is no longer a need for any kind of an opposition…

Mr. Navalny has truly held an important place in the political system for many years with his unique monopoly over the segment of the opposition that refuses to compromise with the Kremlin. But the new reality of Mr. Putin’s lifelong rule demands new conditions. A critic of the regime must now acknowledge that he is not risking a seat in Parliament or even his freedom — but his very life.

The problem is that the system in which you’re either for Mr. Putin or you die seems much more unstable than what came before it. Political terror precludes the possibility of political stability. The person least comfortable in a Navalny-free Russia is bound to be Mr. Putin himself.