DONETSK, Oct. 19 -- Tetiana Montian spent years making Moscow's case, down to an address to the UN Security Council a week before Russia launched its military operation in Ukraine. On Monday a court in Donetsk sentenced her to 18 months in a general-regime penal colony over a single phrase from 2022.

The Voroshilovsky inter-district court found her guilty of public calls to extremism online and banned her from administering websites for two years. Its press release, which describes only the administrator of a Telegram channel and does not name her, says the verdict has not yet taken effect. Her case echoes that of Ilya Remeslo, a Kremlin loyalist turned critic who was arrested in July on army-fakes charges.

What makes the sentence stand...