The Kremlin mounted Russia’s most fearsome nationwide police operation in recent memory on Sunday, seeking to overwhelm a protest movement backing the jailed opposition leader Aleksei Navalny that swept across the country for a second weekend in a row.

But the show of force — including closed subway stations, thousands of arrests and often brutal tactics — failed to smother the unrest. People rallied for Navalny on the ice of a Pacific bay and in the thousands in cities from Siberia to the Ural Mountains to St. Petersburg. In Moscow, protesters evaded a warren of checkpoints and lines of riot police officers to march in a column toward the jail where Navalny is being held, chanting, “All for one and one for all!”

By late Sunday evening in Moscow, more than 5,000 people had been detained in at least 85 cities across Russia, an activist group reported, though many were later released.The large-scale police response signaled anxiety in the Kremlin over Navalny’s ability to unite Russia’s disparate critics of President Vladimir Putin, from nationalists to liberals to many with no particular ideology at all.

But the show of force also made it clear that Putin has no plans to back down. Shortly after the American secretary of state, Antony Blinken, condemned “the persistent use of harsh tactics against peaceful protesters and journalists,” Russia’s Foreign Ministry released a statement accusing the United States of backing the protests as part of a “strategy to contain Russia.”

The crackdown on protesters showed that Putin — who has maintained a modicum of freedoms in the country, including an open internet and some independent news media — is ready to ratchet up authoritarianism in order to avert a possible threat to his power.