PRESIDENT VLADIMIR Putin is apparently not content to harass, persecute, smear and poison opposition politician Alexei Navalny, who has mocked and embarrassed the Russian leader by exposing the regime’s corruption. Now, following Mr. Navalny’s cooked-up political trial, Mr. Putin’s minions have settled on a new tactic: trying to silence and pressure him psychologically.

Russian media has reported that Mr. Navalny, who returned to Moscow in January after having barely survived a nerve-agent poisoning carried out by a Kremlin hit squad, would be incarcerated at a penal colony known for cruel, dehumanizing conditions. No one doubts Mr. Navalny’s personal courage; he knew that in returning to Russia he would face Mr. Putin’s wrath. Now, it is precisely the opposition leader’s resolve that the Russian president seems determined to put to the test.

According to former inmates and lawyers familiar with Penal Colony 2, the facility east of Moscow to which Mr. Navalny has been transferred, it is notorious for subjecting convicts to extreme isolation. That’s especially the case at the camp’s so-called Second Sector, a prison-within-the-prison where inmates may be confined for trivial infractions. There, inmates are forbidden to speak or interact with one another, may not make eye contact with guards and are required to stand with hands clasped behind their backs when not in their cells. Convicts are afforded little unsupervised time, and lawyers representing them describe having to wait for hours to see their clients when they visit the prison.

By isolating Mr. Navalny, the Kremlin may succeed in silencing him for the duration of his 2½-year sentence, which was denounced as unlawful by the European Court of Human Rights. No doubt, that would suit Mr. Putin, whom Mr. Navalny has repeatedly subjected to ridicule, most recently in a YouTube video expose of a staggeringly opulent $1 billion palace on the Black Sea built for the Russian president’s enjoyment. Mr. Putin, who has contrived to remain in power almost indefinitely, may imagine that having Mr. Navalny disappear from public view will quiet nationwide street protests like the ones in January that were met by thousands of arrests.

In fact, those protests were impelled not only by the barbaric treatment the regime has meted out to Mr. Navalny, but also by broad popular disaffection with the graft he has exposed among Mr. Putin’s cronies. That revulsion, along with a stagnant economy, will not fade just because Mr. Navalny is muzzled for the time being.

Not all Russians regard Mr. Navalny as a viable political alternative to Mr. Putin, yet there is no doubt he has unnerved the Russian leader, On Monday, two senior U.N. human rights experts recommended an international investigation of his poisoning, noting that Mr. Navalny “was under intensive government surveillance” at the time, making it unlikely that the attempt on his life took place “without the knowledge of the Russian authorities.”

Most major Western governments have called for Mr. Navalny’s release from prison; on Tuesday, the Biden administration reiterated that demand and, to drive home the point, imposed sanctions blocking top Kremlin officials from accessing assets in the United States. There should be no pause in the crusade to secure his freedom.

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