The Russians who braved subzero temperatures to demonstrate against Vladimir Putin on Feb. 4 were not as liberal as the West would hope. They differed from the participants in last December’s rallies, which involved young and middle-aged professionals. Some of these marchers represented instead an anger that has been brewing for years on the Russian street but has found scant expression in the country’s neutered official politics or on its sanitized airwaves. Some might term these ideologies extremist, but given the dark, brutal conditions in which they have arisen over the past decade, they are only natural.

On Bolotnaya Square, by the iced-over Moscow River, anarchists in black carried banners proclaiming “A Strong Society Needs No Leader”; communists with fluttering crimson standards called for free education and health care; and rowdy young nationalists declared “God is with us!” and “Russia for the Russians!” (pointedly excluding the Central Asian Muslims who have in recent years moved to Moscow in great numbers, searching for work). A few protesters carried Soviet flags: Nostalgia for the Soviet Union’s social safety net and superpower status is strong, even among people too young to have experienced much more than their parents’ reminiscences. Others—people with local grievances, various other leftists, and even die-hard Russian imperialists—handed out leaflets and tried to proselytize the passersby.

The rally’s organizers estimated attendance at 120,000—an astonishing figure, given the weather. This was not, however, the day’s only outdoor gathering in Moscow. Out on the heights of the Poklonnaya Gora park, tens of thousands of Putin supporters assembled under the banner “We Have Something to Lose.” According to press reports, many had been paid to attend or threatened with dismissal from their jobs if they did not; they were bused to Moscow in vehicles owned by state-owned companies and treated to potent grain-alcohol...