After 16 months of war in Ukraine, Russian soldiers finally were greeted as liberators. On Saturday night, they were cheered by crowds on the street, and hailed by passersby who posed for selfies.

One big oops, though. These soldiers were not in Ukraine, seeking regime change. They were in Russia, bent on regime change.

The weekend  coup attempt against President Putin was canceled by its instigator, Yevgeny Prigozhin. Its impact, though, will be lasting. Welcomed by border guards, indulged by Russian Army units, and cheered by civilians, a military convoy of Mr. Prigozhin’s Wagner mercenary group drove unimpeded 500 miles up the M4 highway. 

When they were two hours short of Moscow, Mr. Prigozhin ordered his men to drive back down to Rostov, where he was occupying the main logistics hub for Russia’s war in Ukraine.

“Wagner likely could have reached the outskirts of Moscow if Prigozhin chose to order them to do so,” the Washington think tank Institute for the Study of War said Sunday.

The mutiny, the biggest challenge in 24 years to Mr. Putin’s power, would, the Institute said, “likely substantially damage Putin’s government and the Russian war effort in Ukraine.” Just like the drone that exploded on a Kremlin roof days before Moscow’s annual Victory Day parade, Wagner’s bloodless invasion of Russia has popped Putin’s image of invincibility.

“The myth of the unity of Putin’s Russia is over,” Italy’s foreign minister, Antonio Tajani, told the Italian newspaper Il Messaggero. “This internal escalation divides the Russian military deployment. It’s the inevitable outcome when you support and finance a legion of mercenaries. One thing is certain: the Russian front is weaker than yesterday.”

This may be just the beginning, Secretary of State Blinken argued Sunday on the American talk show circuit. “I don’t think we’ve seen the final act,” he said on ABC News. On NBC, he said: “We’ve seen more cracks emerge in the Russian facade. It is too soon to tell exactly where they go, and when they get there.”

Mr. Prigozhin, a hardline Russian nationalist, distributed a video Saturday deriding official justifications for Russia’s war on Ukraine as fake. Mr. Prigozhin has repeatedly laid charges of corruption and incompetence against the leaders of Russia’s war effort — Defense Minister Sergei Shoigu and the chief of General Staff, General Valery Gerasimov.

On Sunday, Russian state news agency RIA released video showing crowds in Rostov cheering Mr. Prigozhin and chanting: “Wagner! Wagner!” Sunday, the only word from Mr. Putin was a canned TV interview from Wednesday, when he expressed optimism about the war in Ukraine. Mr. Prigozhin denounces this kind of view as delusional. Said Mr. Putin: “We feel confident, and, of course, we are in a position to implement all the plans and tasks ahead of us. This also applies to the country’s defense, it applies to the special military operation.”

Saturday, in an angry speech condemning the mutiny, Mr. Putin compared himself to Tsar Nicholas II and Russia during World War I. For Russia’s leader, this historical comparison is infelicitous. In World War I, mutinies by Russian soldiers contributed to Russia’s military defeat, and to the abdication and eventual execution of the Tsar.

Under the deal worked out Saturday by President Lukashenko of Belarus, Mr. Prigozhin is to go into exile in Belarus, and his 25,000 fighters are to go back to their camps inside occupied Ukraine. Aside from Saturday night’s withdrawal from Rostov, it is unclear how much of this will happen. Presiding over a cult-like operation, Mr. Prigozhin depends on his soldiers’ loyalty for his own safety.

It is unclear if Russia’s defense ministry will try to disarm and demobilize the Wagner men. Desperate for experienced soldiers, the ministry might try to integrate them into existing units in Ukraine. The generals might worry about infecting their ranks with soldiers who already have mutinied. News of the mutiny undoubtedly is already sapping morale on the front line.

Meantime, Ukraine’s deputy defense minister, Hanna Maliar, said Saturday that Kyiv’s troops had “launched an offensive in several directions at the same time.” Ukraine’s foreign minister, Dmytro Kuleba, said Saturday: “Any chaos behind the enemy lines works in our interests.”